I would probably build a Bass with a Rickenbacker style body and a MusicMan style neck. The body design looks really cool, I tried one out but didnt dig the sound. The 3+1 headstock also looks nice. For the pickups I would go for a double reversed precision set up. I liked the sound of the one from FGN, but unfortunately I never could buy one :(
But now to your questions:
- probably oil or colour coating in a simple black
- 4 or 5 strings, depending on where i would use it
- if 4, normal frets and if 5 strings multi-scale
- 4: 34 inch, 5: 34-37"
Yeah, the possibilities are endless and I am also not fully sure what I would want.