2.5volumes works for a lot of beer styles, so that is what I would set it at. Put a thermometer inside the kegerator to figure out the temp then pick the pressure accordingly from that table.
If 10psi gives a lot of foam, maybe your line is too short. How long is the beer line? For 10psi you need like 10 or 12ft to get a decent pour. Search balanced beer lines and there should be a calculator to help you out.
For the short term solution for your buddies, I would leave it at 10psi then tomorrow when your friend come by drop the pressure to 5psi and vent the headspace of your keg and just serve at 5psi for the night. The carb level will not drop that fast.
Long term get your line balanced and just put it on 10 or 12psi and you should be good.