Hi Mik
1 - If you start funding your account with another card or bank account, later on when you wanna withdraw money you can choose between the two (there are certain rules with it). In case you have trouble you can always email the team and they will help you where possible.
2 - I personally prefer to invest in local currency, I started with T212 only in December and at the moment my main portfolio is with another broker with multicurrency accounts. As soon as T212 will offer in specie transfer I will move everything here and I hope in the same time they will have also multicurrency accounts.
In your case I would stick with the USD account for now but funding it with TW or Revolut. And like me and others wait for the MC accounts.
I leave you this thread where was said that is something that will be considered in Q2, but with Corona, the new releases and everything I’m not expecting the team will have time before the end of Q3 at least.