I was working on something like this myself for a while. My thoughts:
* the human-sized boardgame minis are indeed on the small side. Things like the cacodemons, Mancubi, and any other big monsters do fine. The cyberdemons are sufficiently imposing. The sculpting on any and all of them is soft.
* for Imps, I was going to use Barbed Devils from Reaper
http://www.reapermini.com/OnlineStore/barbed/latest/03574. Expensive, but still cheaper than finding any original models.
* For the revenants, I was going with crossing GW skeleton bits with Necron torsos.
* For zombie troopers, I was thinking of the Copplestone zombie troopers for the majority of them, plus some of the old Warzone models. GW Catachan troopers Nazi zombie heads from West Wind's Secrets of the Third Reich are another way to go for the shotgun/HMG troopers that were always supposed to be a little more alert.
* For alternate flying head monsters, I'd suggest the eye beasts from Reaper's Bones line.
http://www.reapermini.com/OnlineStore/eye%20beast/sku-down/77043* And for the biggest, baddest cyberdemon of them all, I did have a go at replicating
http://theminiaturespage.com/workbench/44044/. At least, I bought the original model. He's still sitting in the box.
(edited to add:) Aaah! Found the project I was thinking of: The Iron Dream Tournament! Check this out for Doom-y miniatures action. Many of the models here are from the boardgame.
http://zugrub.chez-alice.fr/negromundheim/IDTV/idt5report.htmlGood luck!