This book would probably be a good start.
I've read some of the author's other books, and articles and they were all very good.
And the book is very reasonably priced.
Some things to keep in mind. There are HUNDREDS of mayfly, caddis, and stonefly species in PA streams.
Some flyfishers get way deep into that, because they find it interesting.
But it is not necessary to do that to get good at catching trout on flies.
You can catch a LOT of trout using common generic patterns, which may not imitate any specific pattern, but instead are general impressions of numerous insects.
Then carry specific imitations of the MAJOR hatches of the streams where you fish.
Even though there hundreds of species in PA, my local stream has only about 5 or 6 or so that I'd consider major hatches.
I think overall the number of trout caught on "generic" flies is probably greater than the number caught on imitations of a specific species.
The number of trout caught on flies like Parachute Adams, Wooly Buggers, pheasant tail nymphs, and Walt's Worms is very high.