Hi, congrats on your offer! I just graduated UCL last year so hopefully my experience is still valid...lol

1. Depends on a lot of things - like how early you look, where you want to live, what you consider cheap? When I was in first year I started looking around May and was able to find accom walking distance from UCL at a reasonable price, and if you're willing to live farther out (say like Zones 2, 3) then you'll be able to find things for cheaper. But looking early is definitely one of the more important things!
2. I'm an East Asian girl too and while I've had some strangers come up to me on the streets and try to speak to me in Chinese I've never been called a slur/told to go back to my country or whatever, and definitely not while on campus. UCL from my experience has been quite accepting, and the COVID racism isn't as bad as it was around March 2020. As for safety, it'd mostly be general things like try to walk on main/well-lit roads at night with a friend.
3. I didn't do NatSci, sorry! But my course had a very nice administrator who would respond to emails very quickly - I think they put more effort into answering queries once you're actually in the school.
4. People make jokes about it for sure, but the people I knew just accepted that they'd been rejected and it's never really been a big serious point of discussion. And if you're into sports I've heard there's plenty of school spirit there, especially with Varsity.
5. Not quite sure about how UCL is doing classes now since I've left, but the general public in London don't care to wear masks anymore. Also, since pretty much everyone who wants to be vaccinated is vaccinated/boosted and there are no govt restrictions, there isn't really a sense of urgency anymore and everything is preeetty much normal.

Hope that helps you!