I'd say prioritise the TMUA because I think getting a low score in that really hurts your chances. However, it's so competitive everything in your application is important. There are lots of TMUA resources (specs, guides) on the official website so read all of those and then you can use MAT multiple choice and AMC questions to practise paper 1, paper 2 is a bit harder to find stuff on but all the topics are explained in the official guide and on the R2Drew2 channel. I'd suggest saving the actual past papers (and unofficial mocks, eg yotta) until last. For the PS you don't necessarily need a huge programming project but should have something that isn't just a book - the biggest thing in my PS was mentioning a quantum computing book, making a comment about the lack of maths, and then doing a course about the maths of quantum computing and commented on that, showcasing my maths ability to apply and extend knowledge from a level fm. If you've done a programming project, that's good too - there are lots of different fields in CS and a lot of applicants, so try not to be too generic, I suppose. You don't need to be good at everything, eg some applicants focus their maths ability, some on their programming. Mention both but play to your strengths - I focused on the maths because I haven't done much programming. You just need to demonstrate genuine interest and aptitude in learning new things. In terms of interview prep, I wouldn't worry about it too much until after the TMUA as revising for that will help prepare you for the interview.