prior to my discovery of the regularly touted OpenRPG chat/map client, I used a "range" system when running online combat.
Basically, there were a few states of position that people could be in relation: Melee Range, Close Range, Far Range, Penalties Range, Sight Range.
Melee: I can hit you with a sword. also "Reach Melee"
Close: I can shoot you or close with you and still attack.
Far: I can shoot you but cannot close with you and still attack.
Penalties: I can shoot you, but it's so far I'm suffering Penalties.
Sight: Hey over there, I've got my eye on you. And maybe my.. Fireball.
With combatants of equal speeds, they could engage or disengage through single steps... a Far guy could move to Close, a Close guy could move to Melee, and being in Sight range is where wizards tend to go for. Running, double moving, and accelerated movement worked in relation to this system (a 60 ft monk could move ranges twice as fast as a 30 ft fighter, and 40 ft monks simply got a free range every few moves).
Then you get a lil more complex as you wish when it comes to tactics. Flanking things with reach or who are Large (or bigger) without suffering an AoO for moving around too close could require an extra range movement, and generally speaking, flanking is used primarily to prevent reach opponents from doing the "Melee Range-Reach Range shuffle" as well as the actual numerical attack bonuses.
Finally, addressing this in an environment is pretty simple. You can say "Everyone within this room is in Close Range." and "Reaching that opponent will require three close range movements to avoid attacks of opportunity from his henchmen." All you really need is a fair randomization method of saying who is where in relation to others, or give a free range increment to the "point man" (the guy in front is Close to any encounter, while the guys behind, regardless of their exact order, are Ranged, for instance.) Typically you allow the winners of spots and listens choose at what range the combat begins, so melee Ranger scouts may elect to sneaky up and start battle at Close or Melee, while archer Ranger scouts may instead choose to go for Ranged.
It doesn't aim for complexity and it does have instances that, like most systems, will require DM adjudication from time to time, but in chat dnd, getting combat done with in an expedient manner seems king.
As for creative use of environment, sticking to the core shouldn't prevent this or give it any more aid then necessary. A decent option is to have each player state the presence of a prop in the room, or describe a facet of it. Depending on if they make the situation easier for themselves or harder, you award an XP bonus (for the harder they make it). In this way, you can tend to see people turning 40x40 rooms into deadly spike-filled arenas where automaton monkeys hang from spiked chains throwing acidic lead poo at combatants. Good stuff.