Long posts are nothing to worry about, but try breaking it up with proper sentence and paragraph structure. That helps everyone read with comprehension
Now, back to your quest. It's really only has hard as you want to make it.
1) Pick your furniture.
The reason I list this first, is because these are the parts that essentially don't matter. They are going to fit on any AR you decide to build. Pick a stock, and be sure to get a matching buffer tube assembly. ie, you'll want either a commercial stock and buffer or a mil spec stock and buffer. Which one is irrelevant, as long as they match.
Pick a grip, you'll prob ably get a standard A2 pistol grip with your lower parts kit, but most guys simply toss it in a drawer. They are essentially worth less. I don't mean that they are bad, just that if you tried to sell it, you wouldn't be able to. There are probably a few hundred of options so start looking. What you want will depend on your purpose, (as will all these parts)
Pick a hand guard. Carbine, rifle length, extended etc etc etc. Strait tube, quad rail, modular etc etc etc.
For the best accuracy, you'll want something free floated. Some choose carbon fiber for weight savings, but you're only going to save an oz or two over aluminum, so that's a dumb reason to me. The only benefit to carbon fiber is that it doesn't get as cold on your hand in the winter.
2) Pick your lower.
Either complete, which will come ready to roll, but it seems you don't wanna go that way. You can go with forged which is probably the most common, or billet which just "look" cleaner and more modern...yet more expensive. One nice thing is that you can get a MATCHING billet upper/lower set that look really nice together.
3) Pick your caliber.
This is where things get interesting. If you're skilled in gunsmithing, you can chamber your own barrel and truely build it yourself...but most guys are looking to buy a barrel chambered in the caliber of your choice and get a bolt that will function with your new barrel.
Study up on the bolt face options of certain calibers. The 223/5.56 is the standard bolt face for the AR15 (.384") If you want a caliber with a standard bolt face...shop for something with that diameter of case head.
Something like the 6.5 Grendel will take a .440" bolt face so either buy one specifically for that, or open up a standard .384 to the size you need.
The bolt is pretty specific, so you need to know what caliber you're trying to build.
You won't be able to build a WSSM rifle yourself as the caliber is proprietary to Olympic Arms and the bolt/carrier is unique. You have 3 (actually 4) options with the caliber. Buy an upper (or complete rifle) from Olympic Arms. Buy a custom build from Mike at Dtech, or Carl at Accuracy Systems.
With a caliber that runs on a more "typical" bolt face, you'll be able to get your hands on the barrel, bolt or carrier you need.
4) Decide on a "factory upper" or a true home assembled upper.
Just about anything you want in an upper, can be bought from someone else. It's not complex at all, which is what makes it fun to assemble, but it's where the most gunsmithing knowledge is needed, which is also why most guys choose to just buy an upper and build their lowers.
5) Pick your parts
You can either get a complete parts kit which will include everything you need to complete your lower...or you can get a parts kit "less the trigger group" which just means that you have the option of buying your own after market trigger without having to spend money on a factory trigger you're not going to use anyway.
For most first time users, the factory trigger is just fine, because you don't know what you want or don't want.
If you already know that the factory triggers are bad, this is where you can go wild with either a high end unit or a drop in style in either adjustable or not, and either single or two stage.
6) Shop shop shop.
Everything you need can be had from more than one place at different prices. As long as your patient, you'll be able to combine shipping, get coupons or discounts or even score some freebies.
If you rush, you're going to end up wasting a lot of unnecessary money.
I think that's a pretty good start, but I'm sure I forgot a few things in there somewhere.
The lower is actually really really really easy to assemble once you've done it 2-3 times.
