General

Does STR give more hp/def than DEX or LUK? Or is it all the same?

I started luk dex then str

@Althazir @iEvanMaster Thanks a lot!

Basically what Althazir said.

330 each in STR/DEX/LUK. Either put the rest in the stat you have the most % of, or do what I did and balance everything out if you're going to be recubing a lot.

The AP will be distributed automatically according to what level of multilateral you're on. As such, the effects of multilateral that you desire first is what you should first apply AP into. Luk for avoid rate, dex for abnormal status and elemental resistance, and str for stance. It'll make more sense once you see the multilateral skill description.
For xenons, I usually recommend going for luk first, str second, and dex last. Once you've capped at 330 in everything, put the remaining AP into an individual stat that you likely have the highest % of that stat on your gear. The common trend tends to lean towards dumping remaining AP into luk for that extra avoid rate.

Hope that helps!