Travelling or living in another country and using CEX

Hi, i've been offered a few jobs abroad, and I'd like your advice on the legal use of CEXs and tax returns.

I am going to travel and live in another country for months or years, it depends, and I'll change in the course of years or years. I don't want to do stupid things out of ignorance.

So let's say, that right now i am in a country, country A, where i use a CEX, with KYC. Then i travel, and i work in another country, country B, where this CEX was forced to close its operations. Can i continu to use it there ?

Is it nationality that counts when using CEX, or country of residence?

And what about the tax return?

If I feel comfortable in country B, and start living there for several years, I should file my tax return there.