Those sound like good loud outs. I don't think the pistol you opt for really matters that much. I've played through both Extinction maps with a shotgun and did just fine. There's multiple ways of increasing your reload time, but I like Booster because, remember, the Engineer needs someway of increasing his reload speed, as well. I know when with the load outs I mentioned, reloading an LMG is like reloading any other weapon once you are maxed out. That become important when dealing with the breeder. In fact, whatever weapon you use, you want to be able to reload very fast at all times.
Armor was my third choice above for that slot. I called it shield, but I meant Armor. It's really a judgment call, I guess.
Whatever you decide to do, I would upgrade the Armor/Team Booster first - unless you are the Engineer. The Engineer should always upgrade his Engineer skill first. Where you start needing more powerful ammo is the last one or two hives before you go into the warehouse. At that point you start dealing with rhinos and an onslaught of scorpions. Oh, and that disappearing alien? Try to handle him the same way you deal with rhinos - shoot him from behind. He goes down pretty quick, too. If you can, of course, hit the phantom/disappearing alien with the hypno knife. Makes life a lot easier.
Anyway, just keep experimenting with different load outs is probably the best thing you can do. That's what we did. We would give a load out several runs then consider where we were having issues then looked at the perks again.