1) How many kits (rough estimate) would you say you buy in a year?
No idea, really, so I'll have to use the kits/years method from above. Been back into modeling just about 6 years now. Have 1443 kits of all types (armor/ac/sci-fi/figs) in the stash room, plus I've built about 25 kits/year. So 1593/6 = approximately 265 a year. That being said, I've slowed down quite a bit lately...have gotten more into trading for what I want, and have tried to sell one kit for every one I buy.
2) Do you buy a kit as soon as it is released or do you wait a while? If you wait, what's the main reason for waiting?
Absolutely wait. With a couple of kits still to build in the stash (hah!), there's absolutely no reason for me to pay retail for something. In fact, because of my collection I'm able to hold off on just about anything until I can find it for the right price. According to my stash spreadsheet (yep, I've got one too - a big one that I love tinkering with) I'm currently operating at 28.74% of retail. As in 71.26% off. The power of patience!
As far as kits going "out of production", they almost always get re-released...and if they don't, someone will eventually make a new tooled kit. If that fails, I've still got my stash to fall back on.
3) Do you buy online or from a physical LHS or show vendors or combination?
Majority is online sales split pretty evenly between webstores and private purchases. Next biggest would be show vendors (go to 4 a year), with last place being my LHS. I use the term pretty loosely, as their stock hasn't changed much in the past 6 years...and I'm not going to pay retail+ for stuff.
4) If you buy online, from who? (feel free to list more than one if you have multiple favorites)
Based on order frequency (I think) - Squadron, DragonUSA, Spruebros, Great Models, Hannants, Ebay.