If I full length resize brass every time, it will weaken the brass some[.]
You’re new to this, so it is easy to be mislead.
No, properly FL sizing every time will not weaken your brass more than neck sizing only. This is a theoretical falsehood which gets passed around, but has been disproven in the real world by real shooters.
If I neck size only, the brass will be fire formed to this particular find chamber, and potentially be more accurate[.]
Also, you’ve been mislead by this. Top shooters in multiple disciplines have disproven that neck-sizing only will produce better precision than FL sizing. When either are done properly, many of us could prove no difference in group size, but critically for your long range precision pursuit, the increased consistency from loading to loading gained by FL sizing every time is a distinct advantage.
I don't have the expert[sic] to pick one or the other, but would much rather start out with what is "more right" and understand WHY, I'm doing what I do.
For long range precision rifle shooting:
Full length size every time with a bushing die without the expander ball. Set the FL die to offer ~2 thou shoulder bump, no more. If neck turning, pick your bushing diameter based on your neck thickness plus your bullet diameter minus 2-3 thousandths. If NOT neck turning, then you will need to add a mandrel expanding step after the bushing FL sizer. The bushing diameter should be chosen based on your minimum neck thickness to touch the mandrel, then the mandrel diameter chosen to leave the brass 2-3 thou smaller than the bullet diameter. For most brass, expect at least 1 thou spring back here, so a 2 thou under sized mandrel will give 3 thou under neck. I prefer seating on an arbor press for the added sensitivity and to make use of the fantastic LE Wilson chamber type seating dies, but seating in your conventional sizing press is ok also (a Sinclair Arbor press and a Wilson seating die can often be bought for lower cost than some conventional press “competition” or “match grade” seating dies alone).
You will really want to be annealing for precision rifle games. If not, keeping your brass sorted by firing will be even more critical, and you have to be very careful to feel for inconsistent seating pressure when seating bullets, otherwise you’re introducing inconsistency in your ammo. You’ll see variation from one firing to the next as brass work hardens if you are not annealing, so it really is an important step for a long range precision loader to avoid chasing your tail.
Weight sorting brass and bullets has proven to be statistically irrelevant, especially so for precision rifle games. Volume sorting brass has value for some shooters in benchrest and F-class games, but it’s really not a critical step. Weight sorting match grade bullets, in theory, can actually INCREASE the net variability between your bullet batch downrange, as there is very little (aka, almost none at all) correlation between bullet weight and ballistic coefficient consistencies within a batch (labradar Doppler BC detection is super freaking cool).
It’s really not so complicated as it seems, and your brass prep and processing really doesn’t need to be so burdensome. Using Hornady or Lapua brass and Hornady, Berger, or Sierra bullets, FL size with a bushing die, mandrel expand, seat in a Wilson die, and there won’t be anything you can say isn’t right with your process for precision rifle loading.