Firstly, Congratulations on your offer! It is a great achievement you should be very proud. So many people struggle to get one. And yours is from Oxford. They are notoriously picky, so if they think you are good to go, then I am sure more offers will be coming your way. Whilst it is great to have a choice, having an offer is the most important part.
35k+ people alone sat the UCAT alone, some will only have done BMAT so that is a huge applicant to place ratio. So to get an an offer is against stiff competition all wanting the same places. But, once the offers are out, the competitive nature flips. It’s now the universities trying to get the best students to firm them. This is the same with a lot of degree courses / universities. They are now in the game of selling themselves to you. Applicant/offer holder days are great things to go to if you have a chance, and if you have more than one offer then you should try to get to them ideally. In my view you should never firm anything until you have all your responses.
Unis don’t agree with me on this, they want you to firm them asap to give them certainty. The rush now only benefits them. One of the biggest levers they have on this is the accommodation scares, pressures to get halls. It may be true, but it can also be inflated by clever phrasing, or by students themselves creating the hype.
Find the uni/college accommodation policy on applications (often well hidden) and go over it carefully. Is it first come first served, or a ballot? What is the accommodation guarantee, firm and insurance? What are the key dates??
Importantly, Look at costs of second year onwards accom costs. Rightmove or the uni website links. Cost of transport? Many unis, esp London ones seriously subsidise the cost of uni halls in the first year to tempt people in, and then the second year is a shock! If there is a desperate shortage of year 1 accomm it doesn’t bode well for future years.
London can be a very lonely place as people live so dispersed and commute in as it is so eye wateringly expensive. Oxford has a much more community student vibe. If you don’t like that vibe though …. Birmingham is a really good combination of the two, it’s cheaper, and has vibrant, diverse Birmingham on its doorstep.
Arm yourself with as much info and experience as you can and use it wisely. Yes, it is perfectly valid to firm somewhere other than Oxford, but if money is a concern tread carefully !
Good luck in your future career, wherever it starts!