If you go Gator, you won't really need the V tac as you can opt to use a DPMS aluminum float tube versus the carbon fiber for no cost. Jim Clark is a custom smith and they are great to deal with. I'm sure you could ask for just about any option and you would get it. Ask about ordering a V Tac and having ti shipped to them. You can also save $60 on that Gator by becoming a USPSA member (they give a $100 discount to members). A year membership will cost you $40....so the net gain is another $60.
The JP block is a nice feature if you play with A LOT of loads AND you ever go with a lightened bolt carrier to make the most of absolute recoil control. Otherwise, in all honesty, you really aren't going to need it on your gun. Gas blocks aren't that hard to change, but it's not something you can switch from rifle to rifle easily. If you want it, call your smith and just ask if you can ship them one. I know very little about Dedicated Tech, but most everyone who deals in AR's understands how people like to trick them out.
Putting an AR together is easy. I built the thin barreled kit gun above from stripped receiver at the kitchen table with some punches in about 45 minutes on my first try.
Now....I am about to impart upon you overload.... I didn't do this easlier because it's Pandora's box and a lot of information is incorrect at this link. Anyhow....
www.ar15.com
Arfcom is highly skewed to the military opinion on guns and is not newbie friendly. In fact, it can be the roughest gun forum on the net if you ask a question that is the least bit controversial. They hate match triggers, they hate anything but Colts, they hate anything but Aimpoints and Eotechs, they have tens of thousands of paying members (yeah, I'm one).........most of which have never even used half of what they are spouting information about (I'm not one of those). So, please don't get caught in the "gospel" over there. (They have members who have post counts over 40,000........how much shooting do you think those people get?)
Arfcom does, however, have a all the guides and info to make any changes to your gun.
Click me for Guides
Otherwise do a forum search under "Ar15" and then "Build your Own" for anything else.