Hey there! So I've just started me first year at Exeter doing Physics, and thought I might try and help you out a bit! First thing - everyone here is extremely friendly. I haven't met anyone yet that I didn't get along with. While most of the students here are white and from southern England, I've found everyone is extremely inclusive no matter what your race, religion or sexual orientation. There is only one gay bar and I haven't visited it, so can't give you an insight there. However, I'm Bi, and I haven't come across anyone who cares at all, they just treat you totally normally. I would expect any uni to be like this nowadays to be fair.
The city is quite small - I came from a little market town in Suffolk so from my perspective it's great, but coming from London it might feel a bit cozy. However, the really great thing is that the campus, and all the accommodation, is a 15 minute walk from the centre of town.
There is a big student bubble here as 1/4 people in Exeter are either students or work with the uni in some way, so you often run into people you recognise day to day. So far I haven't been bored at all - I've got so much stuff to do all the time!!
The social life here (in my opinion) is great. Maybe not on the same level as Leeds, however there is something to cater for all tastes. There are plenty of varied clubs to suit whatever mood you're in, whether that's dance music in Move, cheesy singalong hits in Fever, indie music in Cavern, live bands in Phoenix, or classic club music in Timepiece and Unit 1. Again, the good thing about the uni and the city being so close together is you can walk to anywhere in the city - you don't need to worry about public transport, and you aren't limited to staying in the campus club like some other unis are because of how far away the city is (like UEA). Also I've never seen any bad or sleezy behaviour in any of these clubs - they're all extremely safe and just fun places to be.
Nights out vary in price wildly to be honest - there are a series of cheap bars and pubs that are popular with the students, and more that are expensive and best avoided. Clubs typically cost £4/£5 to get into, however it is usually free if you arrive before a certain time. Something odd about Exeter is that we start nights out earlier than other places, it's fairly normal to be in a club by 11, and out by 2.
On the non drinking side of the social scene there are a TON of societies you can get involved in, and you'll definitely find something you like. Of course we are also very close to the beach, so surfing is a pretty popular choice. There is also a fantastic sports park on campus and every kind of sport society imaginable if you're into that.
I also need to fire back at the guy talking about Exeter earlier, because the Old Firehouse is fantastic! It's essentially a pizza place (apparently the inspiration behind the Leaky Cauldron in Harry Potter), and serves some bloody great pizza and drinks at decent prices. A pizza costs £10 quid, but can easily feed 2 people because they are massive. It is always busy but well worth it, expect to spend £7-8 quid there on average.
Rent is fairly pricey - probably around £5000-£6000 for self catered, and £7000 upwards for catered. All of that information can be found on the unis accommodation website. There's no big supermarket in walking distance to the accommodation TBH, so to save money your best bet is to do a big shop online and get it delivered, and then top up with small amounts from coop or Sainsbury's when needed.
You also mentioned applying to accommodation in December? Again all the information is on their website, but if you're going for uni halls (which are mostly nice), then so long as you apply by some point in July all applications are processed equally (it isn't first come first served), and you're guaranteed an accommodation offer. So don't worry about that yet.
I found it very easy to make friends here. As with every uni your flat mates can be hit or miss - some flats become best friends, others like mine are friendly but I wouldn't go on a night out with them. I did come to uni with a friend from my school though, so that certainly helped during freshers. However I've made most of my friends on my course itself and the socials that come with it , and because people are so friendly here you can literally tag along for a night out with people you meet in wetherspoons!
Overall I'd say this - Exeter is a truly beautiful campus. There's a really nice relaxed atmosphere here, and everyone is extremely friendly. The uni has many systems in place to help students if you need it, and all the academic staff are happy to help you at any time. The whole place has a community spirit unlike anywhere I've been before. The nightlife is decent and varied, so it's likely you'll find something up your street. Coming from a big city like London it will take quite a bit of getting used to, however I have a feeling you might like the closer, community feel of Exeter.
(Also if you like Harry Potter there's a whole bunch of stuff in the city and in the campus which inspired locations in the books, so that's pretty cool!)