These are way too simple questions that should not be answered here because every person will respond with what they think the best but they will not be able to make it easy to understand for OP since he is a person of his own and our answers are based on our own past. I think OP should google these, he should go check the results of the google searches, read the answers, check the logic behind the answers and then he can make a case for himself and understand how he should do it.

This is mainly for the second question of course, first question is exchange, and that's always debated and you are not going to get a "right" answer for that, Binance is the most used one and there are still people who hate even binance.