Gunsby's advice.
hmm
general recommendations:
i would go with an 18 inch barrel rather than 16 to get just a tad but more velocity.
go with a midlength gas system rather than a carbine because it is not as hard on your bolt and buffer, it runs softer on the gun and prolongs its life
i would go with a Bennie Cooley or other 3-gun style compensator because it will help you control the rifle, flash hiders and many brakes dont do as much for shooting.
flip up sights are good for rear but its optional on the front.
for
optics i would get a 1-4 power scope, lots of companies make them. make sure it is true 1-4 or 1 to whatever power and not a 1.5 or a 1.2 or a 1.1 power optic. Red dots are good too but they dont help you reach out and touch things as well as a scope. the only draw back of the 1-4x scopes is that they have a set eye relief and a set parallax (i think its usually set to 150 yards on most but i am guessing offhand here and dont know for sure, when you look at a scope it should tell you in the specs/technical info) unlike many red dots (lower end red dots are parallax free from 50 yards out and have an inch or less parallax error closer than 50/ high end units are labels parallax free because their error is so minute that it is its as if there is no error at all, you wont be able to tell) but the set parallax and restriction of having proper eye relief is a compromise that i think the magnification of the scope makes up for
as for grips, that is personal taste, i just grab the magazine well, i prefer the magpul angled fore grips better than the vertical style, of course you can hold the vertical style up in its pocket too...
its more effective to grab both the grip and fore-end together and not just the grip.
when i think all purpose, i think of the optic on it; that is why i recommended the optic that i did. if you do plan on using this for home defense then a red dot will work much better
i suggest getting a set of angled iron sights that fit on the gun at a 45 degree angle to use with the scope, that way you have the best of both worlds...
if you plan on using it for hunting, i suggest only using it for varmints and small predators. its not a big enough round, in my opinion, for hunting deer or putting food on the table. if you want to hunt deer get a upper chambered in 6.8 or a 30 caliber derivative
now for some specifics:
list of companies that make 1-4x optics:
Trijicon's Accupoints, Burris Tac30, Millet, Meopta Meostar, and Weaver to name a few (these are the most popular of the non insanely priced ones)
if you dont want to spend the money on the Accupoint then i would suggest the Burris Tac-30 (it is made in china though, if you can live with that, the price is right on it though and the word on the street is that it is good))
and get the best trigger you can afford!
JP makes an OUTSTANDING trigger and its easy to install, Geissele makes a bunch of nice triggers, AR GOLD trigger from PACT is outstanding but costs way too much (i have one and love it but it is not necessary), at the bottom of the triggers i wold suggest is
Rock River Arm's National Match trigger (its a really good trigger for the money)
none of these triggers are bad and all seriously outperform a standard combat trigger.
i think the trigger is the most important part of a gun followed by the barrel/chamber/crown (all part of a good barrel)
i opted for the AR gold trigger (at 250 bucks
) because it was super easy to install and while i like it i would probably get the JP this time around because it is less expensive, although not as easy to install as the gold, it has a nifty installation procedure that is worth it)
(i am kind of a trigger snob though, i am picky and like em fairly light and crisp)
(here is what i built)
i posted it in another thead here recently... sorry about posting it more than once... i just like it a lot
hope i helped some!
(looks like my advice is a little different than Tirod's)