[UnknownJinX]

Actually, if you are not tracking your SS 1LE, 5W-30 Dexos1 is fine. If you track and DD, and you want to follow the manual's recommendation on the oil, then Mobil1 0W-40 ESP is pretty much your only choice in North America. Thankfully, you can get them for a good deal over at Rock Auto. They go for US$7-ish per quart before shipping, and RA shipping generally isn't too bad IMO. Motul also has a type of engine oil that's in 5W-40 and meets Dexos2, so that could be another option if you don't drive your car in the cold.

Regarding oil capacity, if you are doing your own oil change, I would personally dump in the first 8 to 9 quarts, and then slow down and check the dipstick to see how much you actually need. When I did mine, I needed 10.5 quarts to get it to full. YMMV, and usually I just fill any car I own with a quart less than the recommendation before checking the dipstick to see if I actually still need more.

As for when to change the oil, I concur that you should just follow OLM. 3k miles is pretty obsolete nowadays unless you run conventional/mineral-based oil or you track the car like crazy. Any good synthetic oil will last more than 3k miles. I usually just toss those stickers right away if I get them after service.

I changed my rear end oil at 500 miles once, and then I think 2000 miles. I use Motul Gear 300 LS, and I have no issues with it, but some people seem to prefer sticking with the OEM AC Delco stuff. The latter will be the safest choice, though again, Motul hasn't caused any issues. Just make sure you do get the LS variant if you do want to try it; there is a non-LS variant that's yellow/clear. LS variant is green.