Just an idea, but depending on how many people are willing to join in, and seeing as one of your ideas is fighting over a forge world, perhaps players should be split into teams. Imperials on one side, non-Imperial on another. Both side trying to complete their own objectives, Imperials trying to drive off agressors, the xenos races trying to raid/smash/conquer. Not sure how it would work overall, but was thiking maybe some team games would be in order, if we could fit them in time-wise. And all in all i'm not too bothered about games being a little unbalanced, as long as one side has no massive advantage/handicap with the rules you're adding. For example, restricting vehicles (esspecially transports) for me would mean i have to go out and buy more infantry (not that it's a bad thing mind you 
) because i wont have enough models to make up a full infantry list for 1500 points. Just thought i'd point out that whatever rules you decide to put in, you would have to check with players beforehand that they can comply
I think if you're going to limit types of units someone takes, you might be better off doing it by locking off force organisation selections, rather than arbitrarily banning Vehicles or Tanks altogether, like for example reducing heavy support selections, or making compulsory choices for that recon mission you described something like 1 HQ 1 Troops 1 Fast Attack or something
) because i wont have enough models to make up a full infantry list for 1500 points. Just thought i'd point out that whatever rules you decide to put in, you would have to check with players beforehand that they can complyI think if you're going to limit types of units someone takes, you might be better off doing it by locking off force organisation selections, rather than arbitrarily banning Vehicles or Tanks altogether, like for example reducing heavy support selections, or making compulsory choices for that recon mission you described something like 1 HQ 1 Troops 1 Fast Attack or something