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The LaRue barrel is an incredible deal on sale. I would buy it now. Get M4 feed ramps, your upper selection will be much easier. If you don't want to spend that much, Ballistic Advantage and Faxon have very good barrels.
You don't need top tier parts for a very reliable rifle. LaRue barrel, PSA lower build kit on sale (I think $90), LaRue trigger, or Geissele if you want to spend a little more. ALG makes a very nice trigger if you want a single stage. Nothing wrong with that route at all.
Pick up any lower you want. I like Spike's, but they are abundant in my area. I have a Stag blem that I like a lot as well. Mega is fantastic, a little more expensive, but very nice. If you get a Mega, you will probably want a Mega upper as well. The finish will look a lot better together.
Aero uppers can be had at good prices. Look at Primary Arms and Aim Surplus for a wide selection of handguards. You can break a budget with handguards, or you can come in under budget and still have a quality piece. This always seems to be where I have to decide how much I want my build to cost. I always put the most thought in to the handguard, even though it isn't ultimately that important. Free float can be had cheap, or you can go all out and get a Daniel Defense Lite Rail, which is my favorite, but it's expensive.
Decide if you want optics or not. You should always get familiar with a platform on iron sights. It sounds like you are fairly new to ARs, so fixed sights would be a good option until you master them. My favorite is Rock River Arms fixed rear and Daniel Defense fixed front. Magpul makes affordable flip ups, but as I said, you will benefit mastering iron sights first. If you plan on keeping iron sights forever, getting a barrel with a front sight base installed can be beneficial. If you want to go that route, I would order from Ballistic Advantage. They will pin a front sight base to any barrel that isn't already pinned for a low profile gas block. This will limit your rail length, if you want your rail to cover the majority of your barrel, a front sight base isn't a good option.
Things people break the bank on that I don't think are necessary are fancy receivers, gas blocks, and muzzle devices. Standard forged receivers, A2 bird cage flash hider, and a standard low profile gas block are really all you need. A Daniel Defense or BCM bolt carrier group is nice, but a cheaper PSA premium or AIM Surplus should be fine for just about anything. Most places like AIM and Rainier Arms, for example, also have their own low profile gas blocks these days. They are affordable, and everything you need out of a gas block.
For stocks, the M4 stock that comes with the PSA kit is fine. I don't really mind them. Most of mine are SOPMODs. Magpul makes good stocks, but they don't really work for me.
You don't need billet ambi receivers, fancy lower part kits with ambi controls, muzzle brakes, or expensive stocks like the UBR. They aren't entirely unnecessary, but a reliable build doesn't necessarily need them.