1: I don't know. I bet it all depend on the OS that will support the PowerVR. If it doesn't. then what point of doing it. If it does. I would says go for it. as long I'll able to add other gfx card down the road with out messing up the system.
2: At this point. it shouild work with all amiga OS that comming out. If it had to be one at a time on OS for this system. Just pick what ever is ready and less buggy. You can't sell if very buggy system.
3 Life must go on and price have to come down. So add another non-standard just add up the cost and may not be used.
4 I'm not so sure about it. Forget about the amiga mouse. Newer mouse are better and price are dropping as time go by.
5 Just use the USB and PS/2. Forget about the amiga 4000 connector. Keyboard are cheap.
6 If your thinking about building the whole system, not just the motherboard. I says what ever you can find to keep the price down. I don't mean you rebuilt the keysboard If something are already done.
7 If the OS support the PowerVR 2 or PowerVR 3, I would says go for the PowerVR 3 to be on par with times when it ready to release. If the OS doesn't then don't bother. Keep the price down.
8 Many user are mostly customs case. I'm sure many rather just get the motherboard it-self. For me, keep the price down and use the standard lay out to fix in standard case.
9 I really can't say. I prefer try to keep the price like the Peg and A1. but keep try to keep it low as possable.
10 I really don't care about the name. I just want a working system.
11 Look at number 10
12 I really dont know what your planning in the market. that would depend what your plainning to do.