Kieren:You would probably get better results in the forum but...
* It's a good idea to run a timed 5k 2 weeks or a month before the handicap. No sandbagging, everyone must try their best and these results will help you form the list of who runs first to last and the time between each person.
* Failing the above, you could use a runners previous times over that distance
* Failing the above, you could calculate race from race - there are loads of web calculators out there to do that.
* On the actual run you will have a list knowing who goes first (the least fast) and and how soon after that person the next person runs. You'll need a hand readying runners - they should know how soon after the start they are too run to stop them milling around & also so they can be warmed up
* It's nice to run a course they know. If they don't know it, maybe have a lead bike or sawdust arrows to mark the way.
* The finish area will need lots of volunteers - the aim of a handicap after all is so that everyone finishes together. The Parkrun franchise and most cross country races will have funnels to keep finished runners in line. People will need to bark at them to keep them moving and a person at the end will give them a disc or numbered token to record their position.
* At the finish line someone will record the time. A stopwatch that records splits should do - obviously it will need to do at least as many as there are runners. At the most basic, someone can write down times as they come in, at the more advanced, you have a TAG timing system or even RFID type things.
* The slowest people usually finish first as they are usually new and see the biggest improvement from training both in fitness and pace judgement. Being chased helps then dig deeper.
* I organised a 5K handicap as an out & back route along a beach in Spain a couple of years ago between 9 friends. It was a great way to get everyone on a more even playing field. We ran the route as a normal 5k race to set the handicap 2 days before.