Purpose drives the train,
@Annihilator 
- for me, every purchase is filtered through that viewpoint, and it's literally everything from firearms to luggage to even purchases for my lab.
The marketplace for the .223/5.56 AR15 is currently saturated, and there are a ton of choices available for the buyer. Whether it be the purchase of a complete firearm, pre-built upper/lower components, or even if you want to "build out" an upper, lower -or both- by yourself, there are myriad choices available to fit every budget and every need.
However, the components are not "LEGOs," and one should be aware that there are many finer considerations that can - and should - come into play if the end-use is not solely/exclusively for hobby purposes.
Since you have the time,
@Annihilator , I would recommend that you take a step back and get reacquainted with the genre via the following two videos.
The first is the late, legendary, Pat Rogers' very last recorded lecture about the platform:
Pat Rogers Final Speech, via F3 Tactical
^ This man is a true SME ("Subject Matter Expert") of the platform, and the expanse of his knowledge as well as his passion - even this long after his passing - still resonates within the industry throughout the nation (even more pervasively here in the eastern Midwest), with some of his disciples being among the biggest names (and SMEs in their own right, such one of the heads of Forge Tactical, John "Chappy" Chapman, and Dave Laubert of Defensive Creations, APG member and listed among "The Top 25 Gunsmiths in the US" by American Handgunner).
The run-time on Pat's video is just over an hour, but his lecture style and material have been perfected through decades of teaching: you'll barely notice the time fly by.
That said, the next video does take a bit of intestinal fortitude to work through:
P&S Modcast - AR15 Manufacturing QA/QC
^ It's four hours long, but trust me, if you really want to put together your own AR, it's worth the listen.
This gathering of P&S-vetted SMEs in that sector of the industry really goes to dispel the myths commonly heard/read in the "AR world," even among professional circles. While a lot of the talk does get rather technical and can sometimes even be dry, the payoff for the knowledge that you'll gain from it is, in my opinion, worth it.
It took me about a week to make my way through the video, but I've since re-watched it a handful of times thereafter. It really, really is worth the time.
This P&S "gun nerds" video above will also give you a framework to better understand the videos uploaded by Chad Albrecht of The School of the American Rifle (SOTAR). SOTAR came to the fore in the last few years, after the lamented passing of the noted SME William Larson - aka "iraqgunz" on the M4Carbine.net Forums. The man behind Semper Paratus Arms, Larson was among the first make armorer-level knowledge available to us average-Joes/Janes. Not only did he hold open-enrollment armorer's classes, he also routinely dropped knowledge bombs on social-media platforms such as M4C.net and Facebook (
https://www.facebook.com/SemperParatusArms). Below, I've linked the SOTAR YouTube Channel, and if you click on it, it should populate the videos in the channel in an "oldest on top" format -
As you view his videos, understand that my impetus for linking his Channel is not to suggest that you - or any other hobbyist - needs to invest the not-inconsiderable money to obtain the various gauges and other specialized tools/instruments he uses. Rather, my goal - as with citing the above marathon of a P&S Modcast - is to hopefully help fellow hobbyists gain a deeper understanding of the AR.
Finally, if you like to click around a bit, the AR Build Junkies website is also a great place to get information:
https://www.arbuildjunkie.com