Sounds like a blast for the golfers, but a nightmare to host. Make sure you have a veteran volunteer at each course that can assist the golfers with any issues that arise.
I highly recommend implementing a two-putt max for every hole. If the group misses the first putt, then it is an automatic two-putt. Greatly speeds up the round.
Your goal is to raise money, so sell as much extra "trash" as you can. Usually, you could sell a mulligan and a red tee for an extra $20-$30 donation.
Ask retailers around the area for freebies that you can auction off through an online auction for the event. Most courses in the area should donate a free round to auction off. Golf stores will usually give you free clubs.