Thanks everyone for your comments.
So here are my current thoughts: Get an Amiga 4000 desktop (and deal with the cooling issues). The 4000 will have better parts avaliblilty and it's possible to stuff all the hardware I want in the box. It will most likely be a lot cheaper (still wondering what the cost differences are).
The Picasso IV card looks nice but won't work if I want a toaster system.

The expansion cover at the back of the Amiga looks like a good place to mount the cable from the PPC video card.
I'm still wondering if anyone has suggestions on the Ethernet/Sound options? Are these the best or would there be better options to look at.
Sound - Delfina DSP Plus
Ethernet - XSurf