The below is tailored to the commerical chancery bar, which is slightly different but ultimately does require most of the same things since the work is very very similar between the two.
Firstly university:
1. A first will greatly help you and is probably necessary, but a "top" first is not particularly going to assist you; for one thing you don't normally have to disclose your end degree score and with the way different universities weigh different subjects and things, the end "number" is much less important than the end classification (possibly different if its a 2:1).
2. You want to be a well-rounded applicant, so doing some societies and things you are interested is good. Equally, you don't get your university experience again - there is nothing wrong with making things a bit less frenetic and just applying later. Enjoy your time there. You absolutely will have to do some mooting or public speaking at some point though, so fitting that in at university is often easier with the things they run like novice moots, or just having people email you about external moots which are coming up.
3. Industry work experience is absolutely not crucial. Legal industry work experience is. Even somewhere like the commerical bar, you do too big a range of cases for specific industry experience to help you. It isn't just banking stuff, it will be generic breaches of contract, company law disputes, aviation (possibly), building issues, loans, etc etc.