To add to what Jim said. Anything you decide, have a drivers meeting at the beginning of the day and let everyone know how you're going to handle things. That way people can't try the old "But I didn't know." or "You didn't tell us that." trick...trust me they'll try.
You say this is a club. Who makes the final call on decisions? Do you have a club president? As the RD have them stand with you at the drivers meeting so people understand that you have the full support of the club pres. in any decisions you make. RD decisions must be final. If people can complain to the club pres. or track owner and get your decisions reversed you'll never get the respect needed to do your job.
Does your track have an impound table? It can be hard to get people to use it even if you have one (club races) but they do tend to help.
Flat out tell people in the drivers meeting. "There's no reason for people not to be ready if I give X number of minutes between races. As a driver, if you're not ready, I'm sorry but we're starting without you." Most tracks, and drivers will agree to a '2 minute clock' request if someone has an issue though.
Marshals...they basically get the same time between races as the drivers (you'll always have helpful people out to marshal right away to cover warm up) But if the drivers are all ready and you're waiting on one or two marshals a call over the PA saying "we're waiting on you Johnny slow pants" normally gets people moving. Nobody likes being called out on the PA because they're not doing what they're suppose to be (marshaling). If the between race time is up, Johnny STILL has to marshal AND he gets docked a lap. If he's not out to marshal reasonably close to the start of the race (if you have enough marshals to start without him) He gets to marshal the NEXT race and still loses a lap.
I'm not a RD but these are some of the things I've seen done over the years.