You may want to try an Elzetta ZORM or ZROC Mount. Each comes with Sizing Adapters to accomodate any cylindrical light from 0.7 to 1.1 inches in diameter. They are good to go!
You can't go to the gun shack to buy ammo, that's for sure. I'm all for supporting a local shop, I've purchased a few guns from them but never ammo, their ammo prices are outrageous.
If you are building a lower half and buying a complete upper all you really need is a set of punches or "a small punch" will do the trick and a spanner wrench (cheap). OP it's not necessarily cheaper if you build your own because it depends on what parts you put on there (it can get pricey) but...
For what it's worth, I think I got blessed with a decent EOtech. I have the 512, I haven't shot with it for probably 6 months or longer (new kid arrived and with work and cold weather, I haven't been out to shoot much) anyway last night I decided to pull it out and give all the AR's a lube job...
http://www.digitalmanagement.com/about/careers.php
http://www.catapulttechnology.com/careers/
See if anything looks interesting to you, if you apply, PM me and I will put in a good word for you.
What do you do for a living? If it's computer related let me know I know a lot of people, and have good contacts with very high level people (aka the people doing the hiring).
No I don't believe that the 20 inch bull barrel is needed for 200 yards and in, I shoot at 200 yards with my 16" rifles all the time without issue, but it is your rifle and you should build it the way you want to build it. If you like the 20 inch bull barrel go for it, if not you can get a 20"...
No problem, I'm not really actively trying to sell it but it's been sitting for a long time, I purchased it used, but have really only fired it probably 50 times. I obviously don't know how much the previous owner fired it.
I have the lone wolf 9mm conversion barrel for my G22 and it works like a champ. Actually I haven't had a hiccup with it. But I wouldn't use it for self defense, just at the range. I want my gun to go bang when I need it to.