Should i Play JP

GOD NO.

"Oh God, please open the eyes of this lost lamb."
-Jeanne d'Arc

If you really, really, REALLY want to be ahead of the NA server, go ahead, but
1. You won't get the reruns of most of the welfare Servants
2. You won't be able to enjoy the story (unless you can read Japanese)
3. You will have lower chances to roll for Merlin or Jalter (which don't have single rate-ups anymore)

td,dr: Of course not.

If you enjoy FGO and it's story + can't read japanese.. Then NO, stay in NA
If you only want to play, doesn't care about the story + can't read japanese.. Then GO

I can read japanese a little bit (except Kanji).. And i love the whole story.. That's why i stay on NA, so i can read the dialogue much well

Well— that's only my opinion

Why not both, for me i am a P2P in NA, but i recently started F2P in JP. My JP acct is mostly for me to try out those 3 stars and below for gameplay reason and to try out friends' servants which arent yet available in NA so that I can know whom I like and shd prepare for in NA....

Coincidentally, its a 3 yrs anniversary now in JP so there is a guaranteed SSR gacha and the best part is..it only requires 15 paid SQ.....so I just spent around $15 and got a Tanamo Caster (I nvr managed to get her on my NA acct) and I am really loving her, she allows me to experience a totally diff game play from my NA acct. And yes, for JP acct, I will at most roll only for guaranteed gacha.

Also, other than the guaranteed gacha, now is the best time to try out JP because it is also running 1/2 AP for the story, training grounds plus triple success rate for levelling :) I am now sitting on 800+ AP because of the power levelling due to the 1/2 AP. Farming with Tamo Caster, Mash and a friend's Mama Rikou equipped with MLB Kaleidoscope...

JP being ahead of us would put you at a big disadvantage as you've already missed out on [x] banners, [x] events, [x] SQ/Ticket freebies, etc. Showing up early to a party is fine but showing up late is a completely different story.
-
-
It's absolutely acceptable if you're not ditching your NA account and keeping both accounts alive. This is because you won't be missing out on NA's developments while also enjoying what JP has to offer.