I wish a thread like this had already been started & pinned long ago. Believe me, you're not the only one who's wanted to organize an online race series but just doesn't know where to begin.
First suggestion I have is that you go look at all the other successful race series, and see what they are doing.
Figure out why they do what they do & how it works out.
That's what I did, & if I wondered about anything, I just sent PMs to some of the hosts/organizers of some of the race series, and asked them why they were doing certain things, and for any tips.
Most were very helpful. Many people were eager to describe what works, what doesn't, and why.
Of course it's good to have variety... But on some of the basic things involved in organizing a race event/series... There should be no reason to re-invent the wheel.
Gauge for interest on the general specifics of what you're looking to put together, and then poll for suggestions on the details you're not sure about.
I think the most daunting of tasks involved in organizing a races is the time math involved.
Scheduling a time that's likely to be good for potential participants
Translating time zones
Figuring out laps of a race to fit a certain duration
And of course there's a great deal involved in testing cars for their compatibility - but that's a whole other story.
If you're only allowing a few different cars, which you test against each other, it can make things easier.
One of the things that often would make someone shy away from an event, is wondering if they'll "pick the right car". If you just allow a whole class of cars, for example, there's always going to be rabbits & turtles within that class, and at least a few outliers that would have a distinct mechanical advantage or disadvantage.
Just because 2 cars have the same PP, or the same hp/weight, or are in the same vehicle class... doesn't mean a whole lot once you put them on a track together.
Beyond that, the most crucial of the decisions that will effect who will join and who won't would be the following:
(this is based on what other organizers told me, and I have found to be the case)
allowance or disallowing various aids
tire type & grade
whether or not the cars involved will be running at fully upgraded (maxed out)
whether or not the points system will be set up so there's active competition at all finishing positions
a clear description of rules that will be implemented & followed by all
And then comes the advertising part. Having worked in advertising, this was no issue to me, but I know for most people, advertising properly does not come naturally! (And why should it!)
You should organize your thread's OP in a clear, legible, neat, and informative manner.
Summary of the basic ideas of the race at the top.
Next should be the time of the event, including the time zone (or time zones) for the times listed, as well as a ballpark idea of the duration of the event.
I would put those 2 things at the top, because those are the 2 most important things that determine whether someone's going to sign up or not.
People want to know - what cars, what track(s), what time, and how long? So then they know if they want to, and can, participate, according to their own real life schedule, and online racing schedule.
If it's too difficult or takes too long to find that key information, they may get distracted and move along.
Include a photomode photo of the car or cars to be involved, maybe even on the tracks intended. (yes, it's true - art catches attention & gets people interested!!)
Then clearly define the details, restrictions, rules, and everything else of import, in an easy to read format.
Don't be afraid to use Size, Font, Colours, & Bold, to differentiate, call attention, or
just make reading easier.
No one wants to sift through huge unending paragraphs of run-on text to find pertinent information.
Hope this helps.