Need some opinions/ advice from some of you "gun hands"

My $.02, worth the price paid:
There are a bunch of new rules that affect all states when it comes to 80%'ers. I would avoid them. BATFE has been collecting sales records for anyone selling them and then knocking on doors. They're still legal for now (there's an injunction in place that's stopped a 'ban' from being put into effect), but I expect that if the courts side with Brandon that anyone who's bought them in the meantime will meet some unpleasantness in the future. Some folks are OK with that, and I applaud them, but it's not the right choice for everyone.

Poly lowers are junk. Full stop. The stock attachment point is a weak area and poly lowers fail there too easily. Whether 80% or one of the dumbass factory-made ones, they're not worth using to save $20.

The mfg, cost, etc should be dictated by what you want it to do. Self-defense and life-saving tools should be high quality. Plinkers etc can be cheaper. Quality is mostly tied to price, but there's a lot of 'barbecue' guns on the market too. Look nice, cost a lot, don't function for ****. BCM/Daniel defense/Colt/FN are serious brands. PSA/Aero/Spikes make serviceable stuff that tends to be cheap, but customer service is junk and lots of parts are just 'good enough' and not always 'serious use' quality - doesn't mean they don't work, but it's more likely to fail when it can't. BCM is currently running a special with uppers - buy a complete one, and the BCG (bolt carrier group) is included for free - which is nearly $200 off.

A 14.5" barrel with a pin/welded muzzle device to make it a legal 16" makes for a handy package that is easy to deploy. A barrel shorter than 16" requires an 'nfa tax stamp' ($200 tyranny tax plus a background check that can take from a month to several years - mostly because the FBI suck at paperwork). A while back, BATFE decided 'braces' are no longer legit. The courts will eventually work out what's actually 'right', but no one needs a surprise visit over a $35 chunk of plastic. One of the good things about buying a complete gun is that it's almost certainly going to be a legal configuration in every case.

Metal handguards look cool and work great with accessories like lights and lasers, but they get hot within 30-60 rounds (depending on how fast you fire, they can get too hot to hold without gloves within that time). They're a necessity for the warfighter, but whether they're a good choice for an individual depends on the application.

Polymer handguards can be had which can attach lights but not lasers (too wobbly). They don't get anywhere near as hot, and tend to cost MUCH less. Poly handguard builds almost always have a front sight base. FWIW, I highly recommend a white-light (flashlight) on any home-gun. Target identification is always the shooter's responsibility and should be taken seriously on defense tools. For reference and referring to the sale above, A BCM upper complete with a welded flash hider on a 14.5" mid-length with poly handguard is ~$600, with a metal rail the price is closer to $800. Lower groups are out there and are ~$250 ish.

Red dot sights are getting cheaper by the day. Holosun is cheap sabtaged chinese junk, but they're 'top o the heap' for imports - I'd stick with a real optic (aimpoint/trijicon/eotech), but pricing is rough ($500+). 'Dot' sights can suck with eye issues like astigmatism though, holographic (like EOtech) are better for that, but cost is still a barrier. Holographic also have shorter battery life. My aimpoint sights will run for years with the dot set at an indoor friendly brightness level. Dots are much easier than irons when one struggles to focus on the front sight post.

I'd suggest buying a complete upper and a complete lower separately. There's an 11% excise tax for complete firearms and that's built into the price. If you buy separate, it's up to the buyer to pay the tax - just like we all paid sales tax for online orders before it was compulsory - remember? Just make sure the lower assembly has the right buffer for the upper. There's lots of different buffer weights, and they need to match the upper. H2 weighted buffers tend to run with most everything, but lots of lower groups come with a standard carbine (the lightest). Lightest to heaviest 'spec' designs are carbine/H/H2/H3/H6 (proprietary Colt thing).

There's lots of whiz-bang accessories on the market. Most are great for practicing malfunction drills. Keep it simple for reliability. The modern M4 is a great template that runs reliably in a lot of different environments.