What you “should” do with your build depends entirely on what you’re going to use it for. Home defense, hunting, or range toy? A little of all 3? If it’s a range toy, are you shooting standing at 25m or rested at 100-500m? If it’s for hunting, what are you going after? Formulate a plan based on use case.
Barrel length is all about use and caliber. I personally don’t like short barrels with 5.56 as it generates a ton of noise and flash and isn’t an optimal length for getting the most velocity out of the round (which is what makes it effective.) If you want a short barrel, I’d opt for 7.62x39 or .300blk, both of which are more suited for it (and IMO make better home defense rounds, but that’s a debate that goes both ways and rages on forever.) Short barrels make handling and moving around indoors easier and save weight, both of which are considered big pluses for home defense but aren’t too much of a factor for range toys (unless you’re doing some Taran Tactical-type run & gun training courses or something like that.)
Now if you want a longer barrel (14.5-22",) that’s where 5.56 shines. You said you have a plain jane Ruger AR already which has a 16" and irons, so if it were me, I’d opt for something different than that. An 18-22" heavy barrel will make for a great rested target rifle using a bag or a bipod and an LPVO with moderate zoom (say, 1-6x,) but probably not something you’d want to shoot standing all day long. A thinner 14.5" with a light stock, a dot sight, and maybe a foregrip would be a much different story.
Past that, your accessories are also dependent on use. A bench target rifle won’t have much use for a light, but one’s a big time necessity on a home defense rig. If your build is gonna be for home defense, you’re not going to need (or want) an LPVO at all, you’ll want something that’s quick to acquire a clear and open sight picture at close range, so irons, a dot, or a circle dot. Only saying that because you mentioned wanting both a light and an LPVO, to me those would be somewhat counterproductive to each other.
All things you gotta think about before you start buying parts.
My first rig wasn’t too different from yours, it was a S&W M&P Sport. I eventually set it up to be my lightweight kind of all-purpose rifle, but kept it very basic as it was intended. Run it with a MFT Minimalist stock, a Sig green dot, and a short Magpul foregrip. It’s light, maneuverable, and comfortable. I’ll shoot it out to 100m, but don’t bring it if we’re going any further than that.
I built a second rig from scratch for longer range rested shooting. It’s a 20" stainless heavy barrel sitting on a beefy stock with an illuminated Vortex LPVO on top, and a bipod. Fires the same round, but it’s much longer and heavier especially in front which makes it a lot more tiring to lug around and hold up.
I don’t use either for home defense, so no lights.
TLDR: hard for anyone to give you recommendations on what to run if you don’t tell everyone what you’re going to use the rig for.
