I know nothing about scopes, Anyone know a good one that goes up to 6x or 8x for around $400?
Edit: Also about the bipod and the AFG: They're to be used separately, one for supported shooting, one for if I need to shoot freestanding, I find that the AFG helps me balance heavier rifles. Also, the only thing on it that might be random is the scope, everything else (high quality barrel, two-stage trigger, free float RAS, bipod) work together for accuracy and distance.
You can get an SWFA Super Sniper for about $300. It is the only decent cheap scope I know of.
The KAC FF tube is fine. I have a few of them and they work great. Most people that knock them probably have never used one, they are expensive and not all that easy to find. But, considering you have a 26" barrel, a rail isn't all that useful I feel. A bipod and sling are what you will need for long range, and that will fit any tube.
The flip up sights. Those are very expensive, especially the KAC stuff. I only use the 600m rear flip as a backup on my M4. It has a regular front sight. Those flip sights aren't all that accurate. I know in Call of Duty they are dead on, but in real life, they suck. If you are shooting varmints, forget the iron sights.
The 26" barrel is usually used by competition shooters in order to get a longer sight radius. The extra length, that long anyway, is a diminishing return. Not much extra velocity for the length and weight. Not sure about 5.56, but I'd guess somewhere between 20" and 24" would be ideal.
The RRA trigger is fine. They can use a little polishing if you know what you are doing, but if not, they will eventually break in fine and become a great trigger without the polish.
Here is my advice. And I've built a lot of these rifles and have a lot of experience with them.
1. Barrel. It all revolves around the barrel, you can get junk everything else and a good barrel and still have a decent AR. Get the twist rate for the bullet you'll be using, the length for the situation, and weight based on balance and how long you plan on holding it. Get the best one you can obviously, hammer forged chrome lined for full boogie or abuse, good stainless with cut rifling for accuracy. I like Satern Barrels for accuracy, LMT or Noveske for chrome lined.
2. Trigger. A good simple single stage AR trigger, say a DPMS that has been polished, will get you to 4.5lb pull, nice and crisp. For cheap. I say DPMS because they grind the engagement surfaces, Oly parkerizes them making it impossible to tune them, but as long as the engagement surfaces are cut and not finished, they should be useable. Next up is a decent 2stage. The RRA trigger is fine, again, a little polish job helps. Geissele make great triggers, but unless you know what you need or actually need it, it really doesn't help. Compound this by the fact that all the trigger makers essentially keep their lock times secret, so you really don't know who makes the best one. The answer to this then, is to find the one that feels the best to you. For me, the RRA tuned up feels BETTER than the Geissele. If Geissele had a faster lock time, I'd get it and make it feel like I want. But since I'm left in the dark, RRA is good enough. Some people will cry about RRA making junk 2stage triggers. Mine is eight years old and was used as an SDM trigger for awhile when I was in the army. I am still using it, it is in the third or fourth rifle now, untold number of rounds, and it works fine. Some wear, but it is fine.
3. Having a good bolt and carrier, at least mil spec, is nice. This lends reliability, and can lend accuracy too if the bolt was headspaced to that particular barrel. Finally, a free floating tube is nice for long range shots. It will tighten the group up. At close range, 300m or less, and against human sized targets, it doesn't matter much. But for pinpoint, nice groups, or longer ranges, the free floated barrel helps.
The only thing I can see that makes little sense in your build is the use of a rail on such a long barrel. But that is just me I guess, if it floats your boat do it. And of course the sights. Ditch the flip sights or save them for an M4 as backups for reflex sight or something (shoot, save the rail system for that too!). A 10x SWFA SS scope for $300 and a plain ff aluminum tube will make a great varmint rifle with the rest of your build.
But that rail and those flips are more tactical natured gear than not. Nothing wrong with putting them on there I guess, but it is kind of like putting a blower and slicks on, and then stripping the interior out of, a Cadillac. It'll still get you from point a to b, but... You get my point.
] (instead of buying off the shelf). 
