@Pila
You want to maximize your amount of charged hits to regular hits. GS great potential lies in it's huge burst damage. Hit and run style is a good way to get yourself used to monster patterns, but eventually you need to be anticipating where the monster will be and have a charge ready. It can take a while to master but, working on minimizing your regular attacks and trying to get as many Charge attacks as possible is the best best.
Your best combo is going to be unsheathe lvl 3 charge, side slap, lvl3 charge, repeat. This is because it's the quickest to getting to the next charge as side slap takes less time then the horizontal swing.
On armors/skills, I agree with you, I think most mixed sets look horribly ugly, and you will be fine wearing mostly any armor. I still do have a few mixed sets because they look ok, but some armors I will never wear... lol. In G Rank I'd recommend Helios Z, don't listen to the haters, it's great set, Sharpness+1 and HGearplugs and you can easily gem in any other skill you want. Other G rank sets are Diablos, but I don't like how it looks. I've been using Lagi X and Nether a lot as I like how those sets look and can gem them up nicely.
Mostly you want to be looking for (in no order) Sharpness+1, Crit Draw, Quick Sheathe, Focus, HG/earplugs, Attack Up __, but other skills are also handy such as bombardier or trapmaster as GS has their weapon put away so often, it's not hard to naturally work items into the hunt.
Hope you have fun with GS, it's by far my favorite weapon for the last few games.