1. You must own the base game.
2. There is an SKU that includes both the base game and the expansion in one unit.

About servers, I generally recommend Balmung. It is big and so hard to get on to, but very lively. If you do want to try for Balmung, usually 4am (NA) or so on the weekday is recommended to check for openings.

Welcome to Eorzea and good luck!