Hello,
my name is Eugen and I'm a 3D Artist from Germany. I would like to do this job for you.
Project approach:
1. I would sculpt the bear first, then I would retopologize him to a low poly model. After all I would convert it to .fbx and send the file to you.
2. No I wouldn't. Specially if you will import this character to Unity for game development.
3. 250$, delivery in 5 days.
4. There are a few different workflows for that. To answer the question I have to know what kind of clothes is needed.
5. Yes, I know Unity3D. My answer as 3D Artist is - "Low-Poly-Modeling".
Kind regards,
Eugen