pingolf solves all the problems you mentioned. groups can start whenever if you let them. a novice won't be crushed by an expert as the expert will tend to hole-in-one. if you have access to the game settings, you could increase the balls per game to 4 or 5 and call it par. or make em par 3. you have a lot of flexibility with setting target scores/goals. everyone gets to play all the games or whatever you have made available.