Step one. Talk to a lawyer and some insurance people. No Joke.
If you organize the event, you MUST have yor azz legally covered but good.
Total distance of around 100 miles is what we generally aim for.
Start doesn't matter but finnish should be where the evening's festivities will happen. Need time for a dockside tail gater after the run and public viewing of the boats.
Best option is to have a host hotel nearby for obvious reasons.
As for payouts, can't help ya there. We stopped doing that a while back and ALL the cash goes to the named charity.
We do have 50/50 draws at the event though so someone usually gets some decent coin to take home although oftef a percentage of that prize gets donated back as well.