Would it be better to purchase a gunsmithing kit like say from bushmaster or just purchase tools seperatly?  Will be building at least 2 more by the end of year (no more kits) then maybe an FFL, 10 more lowers and it's off to the gunshows.  Any comments would be helpfull.

I purchased all mine seperately.  They have stuff in those kits that you don't need and don't have stuff you do need.  For instance you'll greatly appreciate some roll pin punches (punches with a little nipple on the end)you will never use the screw drivers.  Get a good set of gunsmith screw drivers (hollow ground or parallel sides) from Brownells.

I FINALLY got the Brownell's hollow ground screwdrivers, after buggering up just about every screw I ever used a non hollow ground screwdriver on.  They make a BIG difference.  
I just ordered the roll pin punches and starter punches from Brownell's, and I got a bench block--looks like a big green hockey puck--for driving out pins.  These tools will make your life MUCH easier, based on my experience with not having them all this time.  

The first time I used the bench block, I just had to laugh.  I was taking my carry handle sight apart.  I put the sight on the block, and it didn't move when I knocked the pin out...which fell conviniently down the hole so I didn't have to look for it later.  That right there made it worth while...I never could find an easy or convenient place to knock pins out.  I guess it's the little stuff that makes these tasks easier than before.  

The roll pin punches are handy but easy enough to do without.  

Enco (http://www.encotools.com) sells a steel bench block for $11 or so, as opposed to the $30 that Brownell's wants.  I also made my own out of a $1.00 hockey puck.

One of those small ball-based swivel vises that clamps to the bench is very handy for securing hammers, sears, etc., while you are stoning or polishing them.  

I just put together one stripped lower.  The roll pin punch set from Midway (about $12) was all I used besides household tools.  I would look into a roll pin starter tool if I were going to do more builds.  

I Would say the amount of AR15 specialty tools you need depends on how many AR's you want to assemble and how valuable is a few minutes saved.  Also you may allready have a lot of what is contained in a 'gunsmiths tool kit'.  

Everybody needs a set of good screwdrivers for guns only, I have a set with wood handles, but the interchangable bit type are good too.  Most of us have buggered up screw heads by using the wrong screwdriver once or twice (huh Fenian).