There's no NUMBER of rounds fired to re-bed the stock.Just when it needs it.If accuracy falls off then that is a indication it needs to be bedded again.
1/2" groups at 100 yards is prefered but you could get better results (depending on the rifle or shooter).
You don't have to remove the receiver from the stock to clean it.ONLY TO REPLACE A BROKEN PARTS.
Bedding a M14 M1A is very difficult unless you know how.If you don't then you should have someone who knows how,do it for you.
I have bedded almost 4500 rifles and can tell you that unless you're experieced,it will drive you NUTZ.
I strongly suggest calling Ron Smith at Smith Arms.You'll be glad you did.He's a great guy to deal with.I don't have a FFL anymore or I would vollunteer my services (that may change as I'm considering getting a license again).