Yep... In the long run, I think you would get at least equal educational value by prototyping some parts of the computer in TTL logic, and then writing it in VH

Yep... In the long run, I think you would get at least equal educational value by prototyping some parts of the computer in TTL logic, and then writing it in VHDL for an FPGA. Then, you could go into far more advanced things like pipelining, instruction caching and even multi-core design... And it would be a lot faster (both in terms of building the thing, and in terms of how fast the processor would clock) and cheaper.