Is it time to get back into the game?

Okay, I have not played as much as other ppl(cleared Solomon) but I would tell you that when it comes to gacha games there is never a bad time to start. Now to play in JP or NA, that depends on you. JP has a lot more content than NA(as you would expect) and a lot of good quality of life changes(better farming spots, the 3/4 STAM you mention). Thereby I like to view JP as a more hardcore/intensive game as there is much to do and takes up more of your time. NA has a lot less content(still a good chunk and we are getting more in a few days) but also very enjoyable. Also kinda notable is that since we are behind Jp you will have access to events that you would have events you otherwise missed if you would start in Japan. So now the choice bounces back to you, it's up to you where you want to be.

I can't speak on if you should play FGO again or no or if you should play JPN/NA. I will say that on NA right now we have 1/2 AP main quests till March 11th. You can really fly through the story if you are up for some reading, it is worth it but I guess you don't have to read everything. Or since it seems you've played before if you can pick up your prior account you can be up to speed in no time. If you are rerolling we are in the middle of singularity specific summons that will offer the chance at some solid servants.

Now's a dece time to start in NA, at least.

I would personally play on NA just cause I don’t understand Japanese and would like to know the story without reading translations constantly. If you’re just starting, then stamina won’t really be too much of an issue for a bit since you’ll constantly be leveling and getting free ap refills.