I'm just finishing up my CFI right now. I'll answer the questions as I've found them.
Paperwork: You have endorsements and things like that. Those are all outlined in advisory circulars. Other than that, it's just knowing how to fill out the time in the logbook and what requirments must be met for ratings.
Hardest thing: For me, it was going through what you're doing step by step. It's been a long time (5 years) since I learned ground reference manueuvers and to be honest, they're pretty automatic. However, it's not that way for your student and you need to explain what you're doing as you do it.
Spin Training: It's fun. The first one we did was like slow motion. I just did what has been pounded into my head for all those years (neutral ailerons, opposite rudder, then break the stall). After that they got really fun, much like a rollercoaster.
Pay will vary by flight school. Some pay the same regardless, some pay only for flight time. Some pay more for one than the other. It really varies.
Good Luck!!