i can only play on my old 3DS
can someone give me some tips before try a 100% NO-OOB run??

Can't think of anything specifically. The game is maybe a little janky on 3DS, but runs pretty much the same. Just do your best!

Risky Shuffling might be a little tricky with 3DS circle pad. Nothing that can't be practiced, but it might cause a little trouble to begin with.