What's the best path to update the game slowly?

Hello everyone! Me and my group have played around 6games in the last 3 years. We are currently comfortable including PoK since about the 4th game. We played mostly with the preconstructed galaxy from the rulebook and haven't read much into any stuff that is existing online. What is the consensus of how to expand/update the game slowly of what is avaible online? What are common tools used (I've heard there are drafting rules) Thanks!