I am in the process of replacing a 38" Neo Angle shower in my upstairs bathroom. A few questions.

1. The old shower had 2 ceramic tile walls on the inside that I removed the ceramic from. I am replacing with a complete fiberglass surround. When I took the tiles off, I obviously did some damage to the drywall, which now needs to be replaced. Should I replace with greenboard, which is what's there now, or should I use a cement board? Or a combination of things?

2. I am having a devil of a time removing the base of the shower, because it feels as though the drain has been glued on. What is the best way to disconnect the old drain, considering I have no access to the pipes from below?

Thanks in advance.

Matt