@nylekenIn
In OGR there aren't many options for CQB. As you've already mentioned, the game mostly focuses on outdoor combat at medium-long ranges and there are no special CQB tools like flashbangs or breaching charges.
In general, I try to avoid CQB by engaging the enemy from a direction they're not covering (e.g. through a window) or by lobbing grenades into the room. But if those aren't viable options, leaning around corners and covering open areas with teammates is about the best you can do. The problem with this is if the enemy covers the exact direction from which you'd approach, it can be near impossible to shoot him before he shoots you (I think the enemy's observance is even sharper in some mods like Frostbite). If that's the case, I think you can cause the enemy to turn in a different diretion by making noise (e.g. loud gunshots) in a position in that direction. Once the enemy faces a different direction, you can lean out and shoot or move and clear (maybe with teammates).
As for CQB firearms, I honestly think that just about anything can work, but I prefer rifles and shotguns (if you play with mods) for their firepower. I don't think suppressed weapons are necessary, but they may help in some situations.