My parties are all completely different depending on what the client wants. Some have 8 friends round for just a file and polish at £8 each. Sometimes I do 5 pedicures at £20 each, sometimes it's a mixture of treatments depending on what the party guests want. If they want waxing or facials I call my friend who is qualified in this area. There are no set rules, every client wants something different for their parties. You need to discuss requirements with the client.
You need to ask how long they want you there for and know exactly what treatments you will be doing beforehand.. Tell them you need notice otherwise they will request the impossible when you arrive, like 5 manis and 7 pedi's in 2 hrs. You can then figure out if you need to bring a colleague on board.
I stick to my normal prices, no discounts, maybe a glass nail file as a gift for the host.