Line nippers are the same principle as nail trimmers, but are specially made for fishing.
I use an 8' 5/6 weight for my bass fishing. My biggest fish to date on that rig was somewhere over 5 lbs, and it went into the weeds several times, but the rod has a stiff butt and I can really pull a fish out of the weeds with it. I also cast monster flies with it without any problem, but I've been fly fishing for a long time. A lot depends on the rod, how good you are at casting, and how you play the fish. A stiff 5/6 will keep a fish out of the weeds just fine if you've got a strong tippet on. I agree with Juro though that it can be tough to keep fish out of the weeds with a lighter rod, and that it can be tough to cast big bass poppers (especially for a newbie).
If you can, go to a fly shop and ask them to try out a 5/6 with a big fly on it and see how you do. Personally, I think I fish with smaller rod than most people. I used a 4 wt this summer for 3-4 lb smallmouth and big salmon when most people probably would have gone with at least a 5 or 6. There's tricks to playing big fish on a small rod, and to casting big flies with it, that take a while to master.