i'm not a bowgunning expert, heck, i hate the bowgun, but i can answer some questions.
mixing and matching parts, that can up like elemental shots and status shots and stuff, sleep bombing, is usually done on alatreon lol, that's the most common, O-o, what happens is that u all bring sleep shots, and the materials to make a lot of them, and A LOT of bomb materials, basically u put it to sleep, put bombs by the head, someone shoots and bang, head gets lotsa damage O-o
You can buy different shots later in the game, you can also make most, if not all the shots, if you haven't noticed, you have an infinite amount of normal shot lvl1 the bowgun is mostly about staying away from the monsters and firing shots, they really shine in groups, where they get ammo that the boss is weak too, and fire those shots at it, like Uragaan is weak to poison, so they shoot poison shots, qurupeco is weak to water, so they'd bring water, and basically shoot it, they also bring like para shots to paralyze monsters, and such, you can probably get a better explanation from someone that noes more about bowguns, but for now this will have to suffice :P