Julian- sorry i didn't reply sooner i just saw this thread.
You might want to look into these guys in Monkton
They have tying classes and could give you some info in terms of popular patterns and a hatch chart for the Gunpowder.
The local guys at the shop can make better specific recommendations, but it looks like you'll have a variety of typical eastern hatches on the Gunpowder including (but not limited to):
tan, olive and gray caddis size 16
Hendrickson (female) and Red Quill (male) size 14
March Brown size 12
Gray Fox 14
Sulphur size 16-18
Light Cahill size 14
Blue Wing Olive 14-20
These are all common hatches throughout the east.
Here are some good patterns to start out. They are popular patterns throughout the world where trout are found, as well as doing a reasonable job of imitating many of insects of the Gunpowder and other rivers in the East. They will also teach you different tying techniques that you can apply on hundreds of other patterns. I would pick a 2-3 patterns at a time and get materials just for them rather than try and get tons of stuff all at once.
In order of difficulty:
Bead head woolly bugger size 8 an easy tie and good to have pattern for high and/or deep water (Skills: bead head, wire wraps, proportions, palmering hackle)
Pheasant tail nymph (with or without a bead head) size 16 and 18 (a small thin nymph that imitates a lot of mayfly larvae including Blue Wing Olives, Blue Quills, and Sulphurs) (skills: nymph proportions, wrapping a herl body, ribbing)
Gold Ribbed Hare’s Ear (with or without bead head) size 12-14 This thicker bodied nymph imitates many mayfly larvae of hendrickson's, march browns and gray foxes and in lighter cream colors light cahills. in dark browns and blacks it's also a good imitation for many of the stonefly nymphs that are active all winter. (skills: nymph proportions, dubbing, ribbing)
Classic wets: Partridge and Orange Soft Hackle and Hare’s Ear Flymph size 14, Lead Wing Coachman Wet these are all good wet fly searching patterns that give a general impression of emerging mayflies and caddis as well as drowned adults. (wet fly proportions, soft hackle collar, quill slip wings)
Emergers: Sulphur Snowshoe Emerger 16 (a very effective pattern for this hatch, also good in blue wing olive 16-18 and hendrickson 14 versions)
Bright Green Emergent Sparkle Pupa 14 (an excellent searching pattern swung through and just below riffles)
There are many different styles of tying, and you can vary size and colors to imitate a variety of hatches. So learn to tie the style, then modify it for your local hatches. But realize you can use the same techniques and style to imitate the other hatches. Here's an assortment of patterns in different styles to cover you for some of the common hatches. Skills you'll learn are in ():
Elk Hair Caddis - tan body, light tan wing 16 (palmering hackle, delta wing, counter ribbbing)
X Caddis - olive body, gray wing 16 (delta wing, shuck)
Traditional catskill dry: March Brown 12 and Light Cahill 14 (proportions, Catskill hackle collar, rolled and divided flank wings)
Sparkle dun: Hendrickson 14 and Sulphur 16-18 (arc wing, shuck)
Thorax style: Red Quill 14 (wrapping a quill body, clipped v hackle)
Poly Wing or Clipped Hackle Spinner for Sulphur Spinner 16-18 or Rusty Spinner 12-20 (spent wings, split tails)
Parachute style: Parachute Blue Wing Olive 16-20 and Parachute Sulphur 16-18 (posting wing, parachute hackle)
Again to drive home the point, you can fish any of these, or other mayfly hatches with parachute, traditional catskill, thorax, or sparkle dun styles of flies in the appropriate size and colors.
Keep asking questions, and hopefully others that fish the same waters will chime in. And check out your local shops and/or any local Trout Unlimited chapters for fly tying classes that's really the best way to get going-- but there are tons of step by steps and you tube videos on the web too.