All really good questions and really hard to give clear answers. On the Brexit thing and access to living in Europe you have as much information as everyone else, which isn’t very much. At the moment everyone seems to be getting their base choices, but I have no idea how long that will last or the time scale for a base choice. You don’t say whether you have been for interview or been offered a job - if so what contract has been offered? If not then why not apply and ask these questions at interview, make it clear that ema is your only option and don’t accept a contract that says anything else?
From the line, it’s hard (impossible) to see the big picture on all these things so good luck with whatever you decide.