Hey JT welcome to the board. Sounds like you're really into it- good for you!
Mosca and Dan gave you great advice- if you can find a local shop you'd be much better off as far as fly recommendations for the water you plan to fish. In addition to all around good flies to have, like Elk Hair Caddis etc and the great suggestions e put together for you, there will be some variation in recommended patterns based on time of year and water type- wild trout in fast mountain streams vs tailwaters vs delayed harvest (stocked trout). And it pays to get locally tied flies to match specific hatches since the sizes, colors and "style" of tying them will have been proven on the waters you fish.
If you’re anywhere near Asheville, you might give these guys a shout, though I'm sure there are some others near you.
There are general "hatch charts" for many waters throughout the US that you can find online- though not a substitute for local advice from a shop, they can help give you an idea of what to expect. Here's one for NC
As you can see from the hatches by month, some good stuff to have would for Aug to September would be stuff to match the Isonychia and Light Cahill hatches and some terrestrials like ants and beetles if you wanted to add a few specific dries to general high floating attractor and general purpose patterns that would be good for fast mountain streams. Mosca gave you a great list to pick from for a general assortment. If you wanted to prioritize a bit based on what's left in the season but the good thing about mountain streams is that fish tend not to be too picky and don't have a lot of time to look things over- generally you can get away with a lot and not have to worry too much about exact matches to naturals.
But just as an example, a local shop might suggest something like:
Dun Variant size 12 (or another a specific Isonychia imitation which will also occur in late spring throughout the east) in place of a Adams size 12 for a bit closer match in general coloration
Cahill or Sulphur Sparkle Dun size 16 and 18 for Light Cahills and other light bodied mayflies that will occur in late spring through summer in the east) in place of a similar sized and light color hackled version of a PMD.
Foam Ants and foam beetles
might be good to add to a general list of high floating flies good for fast water like:
Elk Hair Caddis 14 and 16
Royal or Ausable Wulff size 14 and 16
A local shop can also steer you towards some good nymphs for fast water streams. They might be Bead Head Prince size 12 (also a pretty good Isonychia nymph imitation) Green Rockworm (good caddis larva imitation for riffles) Golden Stone Nymph size 6 or 8, also good for riffles as some typical stuff you'd find in mountain streams.
Black and olive bead head woolly buggers size 8 or 10 would be a good all purpose streamer/nymph to throw that looks like a lot of things, are good for a lot of different water types and are hard to fish wrong. A good fly for bass too.
Scuds are typically found in slow moving spring creeks and tail waters and would be a better choice if you fished water like that in addition to mountain streams.
You'll also notice that small stuff like Blue WIng Olives and Midges will start hatching in Oct- and will be popping through the rest of the fall and early winter. This would be covered by stuff like small Adams, Blue Wing Olives and Griffiths Gnats, and pheasant tail nymphs that Mosca suggested as well as whatever your local guys recommend. There may also be some great delayed harvest type fishing near you with stocked trout where flies patterns may be a bit different - stuff like Zebra midges and egg patterns- but a local shop can get you squared a way. They are a gold mine of advice, so you really should track some down, and are always worth a stop if you come across them.
As far as floatant, you might want to look for a paste type floatant like Gink or DAB to start. Just dip your index finger in and rub it with your thumb to melt it and then work it into the hackle. Heavily hackled flies (EHC, Wulff, Stimulators, foam stuff) tend to be better floating flies in fast water. A key though is mending your fly line to get a good drift- otherwise the current will drag the belly of your fly line and pull the fly under. Here's a good article about it: http://www.midcurrent.com/articles/t...n_mending.aspx
Finally you might also try looking for a local chapter of Trout Unlimited or a club affiliated with the Federation of Fly Fishers. These groups can really jump start your fly fishing career and have casting clinics, group trips to local waters, informative meetings, beginning tying classes etc. You can do a search here: