I'll try not to muddy the waters too much.
"... difference between benchmark primers vs normal primers? Will this affect my load?..."
In to days marker, get what you can get. As you will be building your load/s for each weapon, safety should not be a concern between the two. Who your weapons/loads like each primer many be different. Only testing will tell. Some only like brand/type XXX and think all others are trash. I think the makers are wanting to make the best product they can for the least cost and greater profit. This demands that the products gain a good reputation. Just try not to switch from brand/type indiscriminately.
"... Bullet seating depth..."
The bullet must be seated deep enough that the round will fit and feed into and from the magazines used. Also and very important, unless you know exactly what you are doing, keep the bullet out of the lands and groves of the barrel. As both weapons are AR types, this will not be much of a problem.
The canalure, the ring pressed into the bullet, can be used as a guide for seating depth. My opinion, unless you are having neck tension problems, don't crimp. Load you're first round without any crimp. press the bullet, nose down, into your work bench. Did the bullet slip into the case? Didn't think so.
Remember to keep each bullet types seating depths uniform.
I trim everyone of my bottle neck cases (maybe not everyone but close) for uniformity. For safety, the brass can not get too long. I tend to trim a little on the short side and have never had any problems. Yes, it is a hassle to trim but the greater the uniformity of the loaded round, the better the chance for accuracy.
"... availability of components..."
Again, get what you can get and work with it.
I have used Varget in .223/5.56 loads with heaver bullets. It give velocity and does well. I don't like it overall. I think it creates excessive concussion (out of a 16 inch barrel.) I prefer 748 and one of the 4895s for both .223/5.56 and .308/7.62s.
Adding in your question about Tula and CCI primers. Tula are imported from the old USSR (someplace) and CCI are US made. Price differences, I would think are connected to the point of origin. As to quality.... I only use CCI, Winchester and from time to time Remington primers. Which is better, not a clue, I'm stuck in a rut and like what I get for no enumerable reason. Again, get what you can get, then deal with it.
Only you weapons will know what works best.
I don't load tracers and can't help with them. I do like you view of using them in the winter, as you appear to be in the Inter-Mountian West area and would generally be shooting over snow.
Always error on the side of safety,