[Bongle]

I've never come close to organizing a race, but as an amateur runner and triathlete, I can tell you what the your "customers" want:
1) Make sure the course is measured well! I did a "10k" last year and got a PB by 3-4 minutes over my last 10k time - turns out the course was 800m short. There are particular procedures for how to measure a course, runners appreciate if a course is exactly as long as advertised.
2) Make sure the course is marked extremely well! It sucks running along not being sure if you missed a corner since you haven't seen a marker for a couple minutes. Also, lots of people that need glasses will run without them, so the course markers should be extremely clear
3) Post results promptly
4) At least among frequent competitors, nobody cares about getting a t-shirt. I have more 5k and triathlon shirts than I know what to do with.
5) If you cross major roads, make sure you've got the cops to block traffic for you. It sucks coming up to a road and having to decide between stopping or risking a "I'm not entirely sure if no-one is coming" crossing. In general, don't cross major roads.

It'd be neat if you did something robot-ey, like had your robot "run alongside" people for the last 100m of the finish. This would obviously depend on how off-carpet-capable your robot is. Or maybe had past robots or past banners (if you've got them) displayed along the route (Weather permitting).

Cool idea though, 5ks are very big nowadays. You can probably make some extra money by having a pre-race or post-race kids race, since a lot of the 5k runners will be parents and will probably have to bring their kids along.