If you really want to know about the M-1 Garand, look up the Garand Collectors Association. Their monthly magazine is a wealth of information on serial number ranges, manufacturers, etc.
Another source for Garands, ammo, information, etc is
www.odcmp.com
That's the website for the Civilian Marksmanship program- a good source of Garands, ammo, and information.
The Garand was designed to work with 30-06 ammo loaded to about 45,000 PSI, not some of the hotter ammo like Hornady's Light Magnum stuff. Most loading manuals will label loads suitable for the Garand, and the powders appropriate for the rifle.
Surplus ammo was made to fire in the Garand and is certainly safe, although you might run across some corrosive ammo. As long as you clean the rifle after firing, that's no problem.
The Garand is a lot of fun to shoot, and a wonderful piece of history.