There is a lot more flexibility within the basing of new FOs than there used to be, and this will only improve as the fleet continues to expand. However, I would caution you to be realistic with your choices, as SOU and Brum in particular are a popular choice (God only knows why
), with some of the more remote outposts like Norwich or Belfast easier to get into.
Plan on being at a different base from your preferred choice for at least your first 6 months. Once the first round of bids are done, you may very well get what you wanted. There are a very significant number of people on the move at the moment, and if the BACON deal goes ahead, things will accelerate in that respect.