I am going to stock up on some ammo about 1500+ rounds.

.223

I am thinking about doing a combo of some Federal and some South African.  I know the SA was made in the 80's.

1st Question:

If it is kept sealed in the Battle Packs how long is it good for if it is stored in my closet? 5 years?  10 years?  more??

2nd Question:
I am going to keep 1000 of the rounds stored on stripper clips.  I would like to have all 1000 in one surplus ammo can or 2 surplus ammo cans of 500.

Any size suggestions on the ammo cans?
How should the ammo be arranged?
Anything I should look for/lookout for when selecting an ammo can?

You could probably get all 1000rds into one of the larger .50 caliber cans. I would arrange it flat. When you go looking for a can, make sure it is in overall good shape (no dents, rust, etc), and make SURE that the lid and body mate up well, and that the gasket in the lid is in good condition. I don't really like battle-packed ammo myself. I take it all out and put it into cans. The most ammo I've had at one time was around 4500 rds, and it only took 3 cans to store it all. Edited to add: as long as it is kept in a closet, sealed in a good can, it should be OK pretty much indefinitely. But if a fire should start in your bedroom-HAUL ASS!

My practice ammo in my 1911 is from a couple of cans I picked up at a gunshow.  It is mixed headstamps from Winchester, Federal and Remington, and all says "42" on the headstamp.

The accuracy isn't as good as I'd like, but it goes bang each time I pull the trigger.

My dad acquired 3,000 rounds of LC M193 ammo sometime in the 1970's, we just found this stuff still on its stripper clips and packed in bandolers in the storage room last year.  Its all headstamped '65 and as of yet (1500 rounds) it has yet to misfire and is still going 3190 fps over the chrono and groups about as well as any surplus military ammo.  It was sealed in .30 cal ammo cans.  It seems to have kept well for all those years.

Like these guys said, ammo if stored in a good ammo can in a closet or some other room, can likely last for 30+ years. Also as you buy newer ammo, try to rotate out some of the oldest ammo and use it at the range while replacing stored ammo with the new stuff. This is probably not necessary and only on occassion do I rotate my oldest stored ammo, and only then if I can replace 500rds or more at a time otherwise I just let it be.