Don't take deposits - that way madness lies - you need to ask for money twice.
The cost of the day has to be paid up front by the organiser, the cost of the day has to be paid up front by the attendees. Simple. It needs to go into a specific bank account. If the cost of the track is covered by the attendees, then if you charge a nominal entrance fee for spectators it would be possible to cover third party liability insurance, which may be needed if we're there overnight.
Is there a GolfGTI bank account already established, or would we need something like that? I'm happy to be a 'responsible adult' (signatory) alongside one other, if needed. I *have* run motor sport clubs before (and if this turns into one of them I have a load of useful resources).
Just a suggestion - all the money handling (and requirements around it) needs to be done up front and crystal.