First of all, congratulations on your decison, I wish you the best of luck.
I have never organised an event myself, but have helped in a few. The first place I would ask is the nearest club/ association that does organise events. From there probably move on to looking for public support and permission.
In any case, go for it, and look forward to hearing from your 5k.
Recently running half marathons. Six completed so far. Now looking for number 7. Once I get to 10 I will start thinking about full marathons.