You've decided what to study and where to apply then? Excellent. You were in a right tizz four days ago because you didn't know what you were going to do.
When you ask "What should I do?", I'm not sure what advice you need. You've told us what you're intending to do. What exactly is the question? Would you like an opinion on whether it sounds feasible?
It's difficult to be planning several jobs and a multi-subject degree (which uni offers such a thing? Sounds very flexible) before you even know where you'll be though. Bear in mind that you could get into any of the places on your UCAS form. And even if you've only applied to one uni, you aren't guaranteed to get in. I'd wait to see where you're definitely going, before planning jobs. Whether you can work in those places will depend on whether you can transfer internally (if you already work there) or whether you find vacancies in your desired branches. Bear in mind that those are typical uni student jobs, so competition will be fierce.