You can, if you want, do a LOT of math to figure out every angle for AEQ (if getting SA's with them) and leftover SP's to use for SA's to be absolutely certain to get 10's in all the SA's you want... but it's really a bit much work to nail it perfectly all the time.
Easier is this way; Determine BEFORE you shop (or build) for AEQ which SA's you might accept for the dot in question. Sometimes it's none, really. Some SA trees just don't give you the quality SA's at the end of the tree that other dots do. Sometimes it's nothing BUT SA's with AEQ. Punters and Kickers are like that. I generally have just a few rules concerning SA's and AEQ. #1, the best bargain are the end of the tree SA's because it costs SO MUCH Sp's to raise them up high. Example; the Protector SA for a Pass Block arch OT. Anytime the SA is at the end of the tree it costs you a LOT of SP's to raise it up to 10 because you have to purchase all the SA's in front of it, high enough to get it up that high. Easier to use either an AEQ piece or your CEQ... or use both and never put a single SP into that last SA on the tree. This tactic comes in handy on other dots where the last SA on one branch is what you'd like to have... but it's not in the archetype's 'preferred' SA branch. Example; A Zone arch FS's preferred SA branch is the Coverage so you can get Superior Vision + Change Direction, Swat Ball, and 1st Step. But the final SA in that branch sucks (for a Zone arch) and is penalized anyways. Much better is last SA in the Hard Hitter tree which is Closing Speed... a great SA to have for safeties. Using AEQ and CEQ you can get that to 10 without spending a single SP.
All that I say to answer your question of "should you wait to get SA's" and I do because it lets me get my AEQ finished and my CEQ figured out so I know how I'm going to spread out the remaining SP's. I generally hold all SP's gained past level 60-65, spending ONLY if I can cap a skill for a low amount of SP's (wait until you only have to buy one skill level-up for minimal SP cost). This lets me get the absolute most out of my SP's. And, I agree with the posters above that 60 is fine for Stamina.