Congrats are maybe a little premature, but still in order. You won't regret it.
I joined the GCA, get their magazine and also picked up a copy of the DVD they sell (got mine for free with membership, but I don't know if they still offer that deal). At the very least, they're a good resource, even if you do join some other organization.
The wait times for CMP-related stuff is pretty long, but still worth it, in my opinion. I've seen ammo boxes of M1 Garand appropriate M2 ball at Cabela's, and wouldn't expect to have trouble getting it most other places that sell ammo. If you find ammo, be sure it's okay to shoot in the Garand. Ammo destined for modern .30-06 rifles will not be good for your new gun.
One book I bought was Hatchers Book of the Garand, but I think the GCA's DVD is a better resource, because they take you through a full disassembly process.
Another thing that I found entertaining was to re-watch Band of Brothers after you've gotten a chance to shoot your Garand and clean it once or twice. That may sound silly to most people, but after shooting teh gun, I realized how much practice the actors in BoB must've had, because they made rifle operations look much easier than I have found it to be. I think I enjoyed the series more afterspending time with "the greatest battle implement ever devised"
"...the liberties of the American people were dependent upon the ballot-box, the jury-box, and the cartridge-box; that without these no class of people could live and flourish in this country..." ---Frederick Douglass