Should I make a Stocks and Shares ISA now?

I got 5k in my bank and an undergraduate and currently don't have a part-time job or anything. But I'm rly interested in investing and money and whatnot. There's a lot of hype around the ISA benefits before April 5. If I theoretically put in 1-2k in a stocks and shares ISA and leave it for a few years, it won't collect tax, right?

Do I also have to keep adding money every yr? Or can I leave it be until I have income and can add some more?

Its important to note that any form of investing carries it's own risks. Note that you are not guaranteed returns on your capital when you invest in a stocks and shares ISA.
Therefore, It's completely possible you might lose all (or a lot of) your money. Case in point:
Look at Nasdaq yearly returns, specifically during the internet bubble from 2000 - 2002. If you had invested £5k at the beginning of 2000 into a Nasdaq tracker, at the end of 2002 you would have been left with circa £1300. (source: Nasdaq 100 Annual Returns by Year (slickcharts.com) )
It's crucial you do your research, with careful consideration of your long term & short term goals. Just an FYI.
That said, you woudn't have to pay any tax on your gains from an ISA. You can deposit up to £20k every financial year into an ISA (cumulatively). So if you had £4k in a Lifetime ISA, then your Stocks and Shares ISA allowance would be reduced to £16k for that year.
You can leave it for as long as you want. Generally for stocks and shares ISAs, if you have a well diversified porfolio and market conditions remain mostly favourable, it's advisable to leave money for longer rather than shorter periods of time. Using my example above of an initial investment of £5k, even though you are left with £1300 at the end of 2002, if you hold till 2017 (with no other invested capital) your return should be around £8,300.
Hope this gives a bit of clarity between the risks and rewards of investing.

Yep, it certainly has, thanks! I've made my ISA and just dropped under 1k into the vanguard S&P 500 for diversification because I don't want to move too fast and instead take time to learn about the stock market before deciding on anything else.

It may or may not be prudent, but the S&P 500 index has proven to beat practically every other index and ETF out there for the last decade or so. Especially last year, the returns were crazy. I'm kind of annoyed I didn't make my ISA earlier but it is what it is.
As for ur 2nd Q, the US has literally outperformed every other nation on this planet for years. If you read the FT or Economist, every graph they have has literally showed this trajectory of high US productivity while the EU is lagging behind - though I understand there are other factors besides productivity that contributes to company profits or smth. Thing is, a Global All Cap Index sounds really good as there are a bunch of high potential overseas companies, but I honestly have just started getting into the stock market - practically a newbie, and I have exams to revise for this May so I don't have enough time to go through all these indexes and ETFs. Not sure if I want to stay investing in the S&P 500 for my entire life but it literally is the safest investment so far, in my opinion.

There are a few good channels on YT to watch and learn about investing.
Here are a few I have found interesting and useful:-
Toby Newbatt
Investing Simplified - Professor G (focus on US markets)
Investing Made Simple - Nathan Sloan
Also want to second the advice given above, invest for the long-term- at least 5, and preferably 10 years.
Good blog is 'Banker on fire'

Yep, it certainly has, thanks! I've made my ISA and just dropped under 1k into the vanguard S&P 500 for diversification because I don't want to move too fast and instead take time to learn about the stock market before deciding on anything else.

Its important to note that any form of investing carries it's own risks. Note that you are not guaranteed returns on your capital when you invest in a stocks and shares ISA.
Therefore, It's completely possible you might lose all (or a lot of) your money. Case in point:
Look at Nasdaq yearly returns, specifically during the internet bubble from 2000 - 2002. If you had invested £5k at the beginning of 2000 into a Nasdaq tracker, at the end of 2002 you would have been left with circa £1300. (source: Nasdaq 100 Annual Returns by Year (slickcharts.com) )
It's crucial you do your research, with careful consideration of your long term & short term goals. Just an FYI.
That said, you woudn't have to pay any tax on your gains from an ISA. You can deposit up to £20k every financial year into an ISA (cumulatively). So if you had £4k in a Lifetime ISA, then your Stocks and Shares ISA allowance would be reduced to £16k for that year.
You can leave it for as long as you want. Generally for stocks and shares ISAs, if you have a well diversified porfolio and market conditions remain mostly favourable, it's advisable to leave money for longer rather than shorter periods of time. Using my example above of an initial investment of £5k, even though you are left with £1300 at the end of 2002, if you hold till 2017 (with no other invested capital) your return should be around £8,300.
Hope this gives a bit of clarity between the risks and rewards of investing.

It may or may not be prudent, but the S&P 500 index has proven to beat practically every other index and ETF out there for the last decade or so. Especially last year, the returns were crazy. I'm kind of annoyed I didn't make my ISA earlier but it is what it is.
As for ur 2nd Q, the US has literally outperformed every other nation on this planet for years. If you read the FT or Economist, every graph they have has literally showed this trajectory of high US productivity while the EU is lagging behind - though I understand there are other factors besides productivity that contributes to company profits or smth. Thing is, a Global All Cap Index sounds really good as there are a bunch of high potential overseas companies, but I honestly have just started getting into the stock market - practically a newbie, and I have exams to revise for this May so I don't have enough time to go through all these indexes and ETFs. Not sure if I want to stay investing in the S&P 500 for my entire life but it literally is the safest investment so far, in my opinion.

May i ask who you opened the Stocks and Shares ISA account with, as i'm looking to do this as well but don't know who to choose? Also did you select do it yourself or for them to manage it for you?

If the US has literally outperformed every other nation on this planet for years then why is its GDP/capita lower than Singapore, Switzerland and Luxembourg, Ireland and Norway...?

I'm not an expert okay, but I do study Economics and all I can say is read or watch basic economics videos. One of the reasons is because of population size, density of its cities and the % of high-income earners and corporations moving into these safe havens of low tax. All these countries are literally safe-havens. GDP per capita doesn't say **** about a lot of things. There are so many cons of this measure.

As an economist, how would you measure performance of a country?

Okay I don't necessarily dislike GDP per capita, it's the main measure used by economists for good reasons, I get it, but most of the time, performance can be relative to each country. Numbers and statistics can only go so far as to completely describe a nation's economic performance. In my opinion, GDP per capita + PPP with more qualitative measures such as national happiness or getting more interviews with the wider general public should be used more often, which I know can be difficult to obtain, but I think it's really important.
I mean, so many politicians and economists are praising the current growth of the US economy and incomes, but if you really talk to the working people, they will tell you a different story which cannot be so easily captured by these quantitative measures like GDP per capita.

And the US is outperforming Norway, Singapore, Ireland, Switzerland and Luxembourg on national happiness...?

what do you mean by outperforming, though? Because when I think of 'outperforming', I think about the level of productivity, the % of start-ups being created every year and whatnot. The US has an INSANE amount of start-ups every year. How I see it is that whether or not these businesses fail (because most of the new ones do), Americans are still trying to build a business and, therefore, productivity. I may have given national happiness too much credit as a measure, but if the American economy is resilient in innovation and creation (especially with AI), I view this as the level of optimism around businesses and markets growing.
The countries you mentioned, btw, are such a special grouping which you can't easily compare to any other country. As I mentioned, Switzerland, Luxembourg and Ireland are TAX HAVENS. Why do you think the top corporations, Google, Apple and Facebook all base their European headquarters there? As more high-income foreign earners come to your tax haven of a country, it crowds your population and thus inflates your GDP per capita. For Norway, I don't know too much about it to say anything about it, but Singapore is an economy that can never be replicated. I mean, it's just a city on a single island, which makes it easier to govern. Anyway, I don't like the countries you chose to compare to the US. The US is outperforming everyone else and it is a fact, whether or not that will stay true in the future is a different conversation.
You said you were an economist, what does your work even focus on?