I'm doing the Penang-trip tomorrow (will post trip report after).

Which pages of my passport do I need a photocopy of when applying for the tourist visa? Also I'm gonna have a single day overstay, do I need any photocopies of anything when paying the fine at the border?

Or should I just inform the mini-bus driver about it and let him take care of it (he did last time, but didn't seem like normal procedure).

You only need a copy your passport photo page for the visa.

Nothing needed other than 500 baht for the one day overstay.

If the driver is willing to handle it let him. They normally have a separate office or booth where you pay the overstay so you would be directed there to pay and they will then do the departure stamp and collect your departure card.