Atta boy, you are going to have fun with that rifle.
Check www.odcmp.com for ammo and parts,
also Fultonarmory.com
and deans gun restoration at http://www.dgrguns.com/

Just don't shoot factory ammo through it, it wil wreck the oprod. I've used Winchester white box ammo which is a 147 gr. load, which I believe is an M2 ball equivalent. You need to shoot M2 ball or handloads through your M1, nothing else. You can get an adjustable gas cylinder nut (its the nut with the big '+' slot in it on the end of the gas cylinder, which will allow you to shoot anything through it for around $40.

Slings and clips can be bough cheap at gunshows- web slings usually go $5-10 and clips usually $0.50- $1 each.

As for the age, it was made (at least the receiver was) in oct-nov of 1942.

http://www.jouster.com/serial/serial.html

Check out the M1 page of Jouster.com There are alot of M1 experts that post there who work for CMP and also various outfits that rebuild M1s. You will have no problem getting any M1 questions answered there.