First fursuit head. I have some questions. s:

So I will soon be starting my first fursuit head, and I'm a bit excited.
I have some questions to ask before I start. I actually got a fursuit base from a suit maker, and I'm going to go off of that. However, it still needs the mouth carved out before I can start.
Here are my questions. Err...

1. What is the best tool to carve out foam? I don't want to mess up because I don't have any actual foam myself.
2. There is no foam covering the back of my head, so should I put any there?
The base has a balaclava attached to it.
3. When I do fur it, should I sew the back together or leave like a zipper or velcro or something?
4. I need to make two little teeth for the top. What would be the best clay to use to make them and how should I attach them?
5. When furring the head, should I just glue the fur directly onto the foam? (I know that you're supposed to sew it together and stuff beforehand. xp)
6. Should I put in the eyes, nose, teeth, and fleece inside the mouth before I fur or after? The nose I'm pretty sure is before, but I thought I'd ask about the others.

I hope this isn't asking too much. I just want to do everything correctly before I even start. Thank you all for the help! <3