goodoboy,

Get the MagPul Slimline handguard. It's M-Lock compatible and gives you a little more handguard length than teh MagPul MOE handguard.

As your AR has a front sight base, I would suggest getting a Mossie Tactical Midnight Mount from Arisaka Defense. I've been using one for years and it's great. It mounts to the front of your front sight and places your weapon light at the 12 o'clock position. This puts the light shadow at 6 o'clock. It also places your light in a good place to operate it. Mossie Midnight 1913 FSB Mount – Arisaka

I don't know what your budget is, but I recommend the Surefire X300. They aren't cheap, but they are light, rugged and throw a beam brighter than anything that small has a right to. I've been using mine for years, on ARs, pistols and in my pocket.

For a sling, take a good look at the one made by Blue Force Gear. I've tried several slings, but keep coming back to the Blue Force sling because of its strength and ease of use. It's ease of adjustment by itself is worth the price of the sling.

If you cannot afford the price of an Aimpoint, get a Primary Arms Micro Enhanced with the dial illumination control. Optical quality isn't up to Aimpoint standards, but it's rugged enough to last and surprisingly, battery life is measured in years. You would be better off if you can swing the price of an Aimpoint Pro, but if you can't the Primary Arms Micro Enhanced is worth the money you'll pay for it. The same cannot be said for many of economy brand red dots.

Every house defense rifle should have a weapon light, RDS and sling. In order of importance-
1) Weapon light. If you cannot see and identify your target, you cannot shoot safely.
2) It's a toss up as to whether you should get a sling next, or a red dot sight. A sling makes handling the rifle easier. The sling is the rifle equivalent of a pistol holster. However, a red dot sight will be much easier pick up in low light than iron sights.

Don't worry about the vertical foregrip. It's nice to have if you like them, but are not essential. If it comes down to spending money on a foregrip or a sling, or putting the money towards a light or RDS, get the sling/light/RDS