*Regarding Monster Behaviour*
You know, that's actually a pretty neat idea, I wouldn't mind seeing this.
Pinkies should probably be almost mindlessly aggressive predators, tearing apart anything they can get their mouths on. Including other demons. Of course there should also be barely "tame" Pinkies found in the company of smarter demon variants as their handlers
Similar to RCTW's Lopers. In Doom 3, they were apparently used as food by the higher demon's, as you could see them hanging from the ceiling in Hell, so maybe we could see the process of that fight happening.
Imps should always be minions, but I think they would work well as clever or at least cunning minions capable of working in concert with one another and utilize various tactics as a pack. Maybe even trying to ambush the player and flank you when they get the chance. But really, they would still just be Imps. Nothing too threatening or intelligent, just a bit of basic cunning. Well, unless they're being commanded by something else...
I think they could just get away with keeping it like Doom 3's imp, an agile spider-like humanoid. If they were used significantly less they would make a good bitch demon.
Which could be the perfect role for Hell Knights, as they could make ideal field commanders for hell's armies, able to get lesser demons to perform more complex tasks and work together in different ways as well as carry out more intelligent tactics. Also, it would be nice that if they would crush or brutally beat any minion that accidentally hit them if they were close at hand. Or maybe just pick them up and toss them at the player
I'm not too sure about picking up demons and throwing them, but they could also be the handlers for the pinky's as you suggested earlier. Who knows, maybe if pinky's are larger this time round, the Hell Knights could ride in on pinkyback!
You know, stuff like that. Archviles should basically behave as even higher up in the chain of command, serving as sort of demonic priests or something and preferring to utilize its minions in ways that made full use of its abilities. Which would of course include being able to resurrect them.
They really need to toughen back up the Arch-Vile, D3's was way too easy, and I the original flame attack could look very neat under newer graphics.
Things like Masterminds and Arachnotrons should probably show evidence of using those brain bodies of their for more than shooting guns at things. I'm not exactly sure how but they should show off their technological adeptness and intelligence in some way. And they should fight smart too and seem more controlled and analytical than the other demons. I imagine they would probably be closer to Hell's equivalent of scientists and researchers than proper warriors but they could still use an assortment of technology to be just as dangerous as any if not more so.
Doing spider things would be a good start, they could use metal wire as a web. Perhaps an Arachnotron could winch in from the ceiling using this wire. And send out a noise of some sort to signal some Trites to come in too.
See, idsoftware981? That's how you make a good post.