black and shiny
I'll address both of these.
Yes, this is something that is far more common in our mod. I regularly put enemies on patrol paths, primarily the more humanoid ones---Commandos, Z-secs, Revenants, Arch-Viles, and occasionally Bruisers. I also put regular zombies on patrol paths, but I make them follow illogical, circular patterns that make no tactical sense (to give the impression they're wandering aimlessly.)
On a slightly more serious note, will the demons move around the levels more than they did in Doom 3? In the original Doom, whilst their spawn locations were static, they tend to wander around a fair bit, and they can still surprise you on occasion, whereas I didn't really seem much movement from the demons (apart from a few Commandos occasionally walking back and forth) in Doom 3.
Not 'random' in the true sense of the word. In a given combat scenario, I will often have 2-3 possible enemy set-ups that will have been pre-determined by often innocuous, simple actions and decisions the player made earlier on in the map. For example, the player may come to a door he needs to pass through, but before he does, he has the option of picking up a box of shotgun shells laying in the corner. What I'll do is set up the triggers and other entities in such a way so that if the player goes through the door first, he might fight two Imps in a particular room later in the map. However, if he grabs the box of shells first, he might fight a Pinky demon in that same room instead of the Imps. It's not truly a random system, but it keeps things fresh and unpredictable enough that it should keep players on their toes. Doom 3 actually did this a few times throughout the game, but not very often, and nowhere near on the same scale or frequency as it happens in Phobos.
Another suggestion would be demons spawning in random locations in some parts of the map: this would definitely increase the tension and replayability.