Well, I just started playing harp a few months ago, but I’m picking up really fast - so I need Diatonic Harps in different keys. I generally play guitar and sing in G and E; do I need to get G and E harps? or just C (which I already have) and A - as someone suggested? Please help a humble beginner!
Definitely get an A and you already have a C, And also buy one in G and E.
So you should have G, C, E, A harps to start out with right away.
If you want lots of keys, I would seriously suggest getting a seven key set in your favorite model! A set of 7 Bluesband is about $40, and the 5-pack Special 20s are $140. Depends on what you want in life!