Often 1/4 to 1/2 is vested immediately. Typically you will have accelerated vesting in the event of an acquisition. This can come in the form of a single or double trigger (first trigger is when the acquisition happens and second trigger is if you are fired or quit from the acquiring company).
Assuming your non-immediately vested shares have a one year cliff (no vesting until 1 year worked) and 4 year vesting (month by month after the first year), you should consider not having any vesting in the event of an acquisition.
Acquisition probably won't happen until you've been going for a couple years at least, and much of your shares were vested immediately so fractional vesting of the balance won't make a big difference to you. On the other hand the fractional vesting might make a big difference to an executive you hire between founding and acquisition and you can assume that a big time hire will negotiate to match your accelerated vesting provision (might really erode the value to the acquirer to not have that exec with golden handcuffs).
If you have FF shares, those should represent 1/4 to 1/10th of your total holding and you should make sure that these shares are all vested immediately at founding.