It is also helpful if you have someone whose musical judgment you trust--wife/GF, nonplaying muso--anyone who is not distracted with either playing or with the function itself (which is why you wouldn't ask the host)--to help with sound in terms of reporting to you on balance, tone, and overall volume level. Get them to do this at intervals before you start (that's your sound check) and during the first set. They will need to walk around the space while you are playing in order to get a meaningful read. Do this two or three times and you will have about as good a setup you can without having an actual soundman. (And it's BETTER than having a soundperson who doesn't really know what they're doing.)

During sound check, dial in the FOH (front of house) sound first with the monitors turned all the way down, then add monitor to fill in what you can't hear from the mains. Unless it's a really weird stage setup, for a party that small, you shouldn't need much in the way of monitor levels. It's easy to go crazy with it if you've never had proper monitors before.

Make a checklist and check it off as you pack so that you'll remember everything. Have spare cables (mic and speaker (for which you can use instrument cables in a pinch)) and maybe an extra mic or two on hand, just in case. Take way more extension AC cords and outlet strips than you think you could possibly need. Have duct ("gaffer's") tape with you to secure any cords or cables that must run across the floor. Have a LOT of duct tape with you.

Tell us more about the system and the room as you get closer to the function, and we can give you more specific advice.

R.

"My primary musical instrument is the personal computer."