Oof, you are asking a not easy thing...
I'm currently busy designing proper boards for the Avalon ASICs, as I found the original ones grossly, grossly inadequate. Avalon is a design which combines the 1970's simplicity of protocols and communication with more recent 110nm TSMC G process (G as for general use).
I'm doing the design phase, as I can do that... one friend is so far the major would-be investor, and is in charge of obtaining the Avalon chips as soon as they appear anywhere. I hope to have HW and SW ready by then. The system is to be properly cooled, not just the laa-li-daa system it has in the original modules.
Oh.. the 'investor' is a friend of slush, so he would be the one to talk to about running a proper operation.
What my design aims is to "maximize the potential" - as much as that is a buzzword, it is part of the economy. A chip that does 280MHash/s on 1W of power is much less worthy than a chip that does 350MHash/s on 5W of power. Even then the ratio is good enough.
I have a long history of cooling and power supply designs, use, tuning. I'm adding high-speed circuits on the go. Overall, the module I'm designing will remind you much of the IBM bipolar mainframe era, it just won't have modules filled with helium.
What scale operation (Ghash/s) are you looking for? Or would you rather be interested in scrypt?