I'm in the process of building a workshop in my basement. I was planning on using Rigid foam boards, glued and taped to the exterior walls. I was going to use spray foam to seal the top and bottom of the boards. The plan is to than put up 2x4 walls in front of the foam, and than drywall.

A few questions.
Is it necessary to fill the cavity with fiberglass insulation ?

I was also going to fit foam along rim joists and wanted to know if those areas should also be covered with drywall.

Also, do I need to put in fire blocking, and if so, where and how ?

I could post pictures of the area if that would help.