What will happen if I have zero balance in OCBC Frank saving account? Will they still deduct or bill fall-below fees to me?

According to CS for 360, they will not deduct a fall below fee for zero balance accounts from it or any other OCBC accounts and close it after 6 months of zero balance. Believe your case may be similar, but you can send them a secured message to confirm this is indeed the case.

Yes they deduct a penalty fee of $2 if your account falls below $1000 after the age of 26. POSB has a lower fall below fees of $500.