I assume like JSE necks the augments cap out at 20 for NQ, 25 for +1, and 30 for +2.
People are reporting that the NQ and +1 can go to 30, at least that's what it shows on the piece. I'm not sure if anyone has reported actually capping the augments on a +1 piece. Good news is that the augments transfer so you can always upgrade later (but it costs 1 extra gem).
Do the +1 augments have value given they'd be missing 2-3% triple attack?
See above, but basically the +1 is "bridge" gear I guess, until you can get the +2 which is just objectively better, augments aside.
Seems as though Head, Hands, and Feet might be most reasonable while +1 body and legs are more difficult to make an argument for?
Personally, if it weren't for the units/matter costs, I would probably 5/5 the set. The accuracy is absolutely insane, DT and meva are insane, and the TA is
much stronger than the DA on Sakpata. There's no contest, in any slot, IMO. You could possibly argue for 8 STP 6% DA on hands being similar to 7% TA in terms of TP gain rate, so maybe Sakpata Hands R30 are better/comparable. The rest are just flat-out worse.
That's without even touching the fact that the set is 5/5 BiS, perfect DM aug Phalanx received set, and the body is better than perfect DM augs.
It's an incredible set for every job that can wear it.