Hi OP my D1 is in her second year at Oxford, so I only know about there, I don't have any information on Cambridge. (Well DH went to Cambridge but spent most of his time playing cricket (or in the bar) he says he didn't work as hard as D1!)
The most important thing, as others have said, is try not to get too hung up on Oxbridge as obviously both universities are massively over subscribed and most applicants won't get a place. It's important to think about all the other choices on the UCAS form.
There is a lot of information on the Oxford University website: www.ox.ac.uk/admissions/undergraduate you can click through for info on courses, colleges, entrance requirements etc, and importantly the timeline for applications. See what sort of information and support school provides. Our school had a nominated teacher for all the UCAS early entries - so Oxbridge, medicine, dentistry etc. The school arranged a school trip for open days and D1 was able to sit her entrance test at school, she also had to submit work which had to be in pdf form with a covering form from school. She was supposed to have a meeting with the teacher to sort this, but got missed out. The deadline was a Sunday and D1 had thought it was the Monday - cue v stressful weekend which D1 has forbidden me sharing details of, haha, but involved her having to break into school
So make sure you check the dates...
You can study MFL with other subjects, eg English, History, Classics, Philosophy - have a look at the course list which you can click through to on the Oxford website. All the entrance requirements and details of submitted work required is on there too. If you get an offer it will be the Oxford standard offer of AAA.
You can either express a preference for a college or make an open application. The applications are looked at on a departmental or faculty level and they aim to interview three people for every place, at this stage the applications are spread out across the colleges so you may well be interviewed by a different college/s than the one you put on application. Not all courses are done at all colleges - check the course and college listings. D1's History joint is only offered by about half the colleges for example.
Tutorials might not be at your college - it depends on the papers you have chosen. If the lecturer is at a different college, you go there. D1 has had tutorials at several different colleges as well as her own.
I think Oxford can actually be cheaper than other universities. The tuition fees are the same everywhere, the accommodation costs at Oxbridge may be less as the terms are shorter, also a lot of stuff is subsidised - D1 gets free admission to the University sports centre for example as the college covers the subs. She lived in college for first year, it was about £1.4k per term plus hall catering credit on her Bod card. The disadvantage is that the rooms have to be cleared in the vacs, there may be some college storage space available. She chose to live out this year, her rent in a shared house (walking distance from college) is just under £600 on an 11 month contract. She will be back in college for 3rd year. Accommodation costs vary, it can depend on size of room, ensuites etc. It's usually sorted out by ballot.
In addition, there is a very generous bursary scheme - if you apply for a maintenance loan you will automatically be put in for a bursary, these go from £500-£5000 depending on household income. These are non-repayable. There is also a travel grant of up to £500pa depending on how far you live from Oxford. Also departmental and college grants and scholarships are available - they are very keen that finance should not be a barrier to study. There isn't really time (and you are heavily discouraged) for part time work during term. A few of D1's friends do a bit of online tutoring.
Have a look on the colleges link from the website, you can see facilities by college, eg gyms, music facilities (eg one has connections with Dansox ) etc. You can often use other colleges facilities and join choirs at other colleges.
D1 mostly socialises with people at her college, partly because starting in a pandemic meant the opportunities for much socialising at all was limited. She does have friends from her course and in societies who are at other colleges.
I would say try and get there for an Open Day - or see if school is arranging a trip. There are general open days and subject specific ones MFL open day in May
Hope some of this has been useful and sorry if I've repeated PPs.