Is this for a hobbyist setup? Becuase when you do the math on running all that equipment it may be more cost effective to get PC's/ Macs off the shelf.
If you're doing it for the Amiga Factor of seeing what's possible, then GO FOR it. I had a setup similar to that from 96-2005. Complete with 2 toshiba timms, A4000T, A4000HighFlyer, MacG4/G5 and a PC with the VT3 (pc video toaster version)
Those were good times!