Congrats on the purchase of an excellent rifle. I love mine.
For ammo, I am fond of the 147 to 150 gr FMJ/milsurp loads for general use. This is cheaper to get in bulk and will have adequate accuracy for most medium range work. I'll second the WWB 147 gr FMJ, as it is available for about seventy-five cents a round in my area, shoots about as accurate as any other FMJ load I've tried, and is adequately clean and completely reliable in my rifle. I use Federal Fusion 150 grainers for hunting as they shoot pretty close to the same as the ball load out the distances I shoot game with iron sights. If defense is on the agenda, I suppose a 150 gr JSP would be adequate but not ideal. I've heard good things about Hornady 155 gr TAP for that use, but have never tried it.
I have put some of Hornady's 168 gr Match load through though. I was about to put 10 rounds into about 1.5" @ 100 yards from the bench, again, with iron sights. Also heard good stuff about Federal and Black Hills 168 and 175 gr HPBT Match rounds. Guess it is up to you to try out some different match loads and see what your rifle likes. Most people recommend not going above the 175 gr weight in the M1A without some special tuning, as it can adversely affect reliability and lead to dangerous spikes in port pressure, and things like bent op rods.
I use Tetra Gun Grease on my roller-bearing and bolt lugs, as well as the threads to my gas cylinder plug, and a light coat of CLP or Hoppes #9 on everything else. The gas system, chamber and bore, bolt face, and firing pin channel are kept clean and dry, as per usual.
For cleaning, I prefer Otis and the like. The cable systems allow the M1A to be cleaned from the breech, which is always preferable. The M1A doesn't require a lot in the way of maintenance. I'll run a cable through the bore a couple times and take the gas system apart every few hundred rounds and clean it, more as a courtesy to the rifle than anything. And every 500 rounds or so, I'll take the rifle completely apart and give it a good wipe down, again, more to keep myself honest out of habit than anything. The rifle is more of a pain to disassemble for cleaning than a lot of more modern designs, but it doesn't need to be taken apart for that level of maintenance very often, and is in fact, not recommend unless absolutely necessary on bedded models, lest constantly removing it from the stock upset the bedding.
O, and mags--USGI or Taiwan Type-57 20 rounders are the only ones I've tried, and they seem to be the most highly recommended. I've had a couple failures to feed from the Taiwanese mags, but overall, the majority of the 1500 rounds I've put through the rifle has been through the original ten of these mags I bought with the rifle, and they've been very reliable. The two USGI 20 rounders I've had have been 100%. I've heard good things about the CMI 25 rounders but have never tried them, and hear they can interfere with a good prone position as well, so keep that in mind. Some people even prefer 10 rounders for prone work.
Other than that, get a good shooting sling and learn how to use it. And have fun with your new rifle!
