There are 3 quad rail style free float tubes that are pretty good, and won't break the bank:
The Olympic Firsh, the Liberator IIs from Fulton Armory, and the Yankee Hill ones.
I've got the Lib. IIs on one 16", and I just put a YHM tube on one of my other ones...although it's not the quadrail style...it's a tube, with places to mount rails of varying lengths at the 12, 3, 6, and 9 o'clock positions.
I can recommend the YHM stuff wholeheartedly, as well as the Liberator IIs. I've heard good stuff about the Oly, but I don't have any personal experience with them.
They all cost about the same, so it's pretty much a "pick 'em" thing...whichever one grabs your fancy.
YHM makes a standard and a lightweight style; since you're building a tactical carbine, I'd check out the lightweights.
As for the installation of a standard 2 piece tube, there's nothing to it if you have the right tools...an action block, and an armorers wrench. Now, SOME barrel nuts on different float tubes require a 3 pronged wrench, but for most, a regular wrench, a la the Bushmaster or DPMS, will suffice. The action block is a must have, otherwise, you risk ruining your upper.
You can put the front sight right back on, or you could get a picatinny rail style gas block. If you do, my my advice is to get one of the bolt on kind...Yankee Hill makes a one piece gas block and flip up sight that's pretty cool....it kills 2 birds with one stone, at about $ 75...a bargain. It makes for a cleaner look if you're using optics, and you can flip it up for back up when needed.
A 3 piece tube with a jam nut is a little trickier in that it's a whole lot easier if you have the wrench to tighten the jam nut, but I did my Liberator IIs without one...another set of hands comes in very handy there.
The only problem is a post ban muzzle brake if you have one...it needs to come off, and that's beyond the capabilities of most of us. If you don't have a brake, the whole process is really pretty simple, but a little intimidating the first time. Banging the taper pins out of the front sight block is the hardest part, once you get those out, the sight assembly/gas tube just slide off the barrel...you don' have to remove the actual gas tube....it's held in by a roll pin, and it's not going anywhere.
Are you buying the barrel assembly seperate, or swapping one that's already on the receiver?
Here's a pic of the Yankee Hill one I just did...bear in mind, this is a full length tube on a carbine, so it required a low profile gas block. Other than that, pretty basic...tighten the barrel nut, and screw on the tube portion, index it, and tighten the jam nut.