Thank you everyone for your votes, suggestions, etc. I was very happy to receive all that feedback.
I've done some thinking, and some testing, and I think multi-class isn't a path I want to go down at the moment. The V8s and MR18 seem too close for proper multiclass, and MR18s and touring cars just don't suit the same tracks or even the same style of racing. Of course, I will run such events in the club and may change my mind in future. For NOW, however, I will focus on one-type leagues, and I have a few planned for 2015, all going well.
Still not committing myself here, so no promises, but my plan at the moment is to run a V8 Stock Car league next. I'd also like to run touring cars at some point, and possibly even a Kart "knock-out" type league later in the year. Not forgetting F3s too, I'd like to run those. Lots of work, let's see how we get on.