Thanks Mike, fantastic information there, much appreciated.
I'm still deciding what to do boat-wise. I started out thinking something in the 20ft size would be good enough, then quickly thought "well actually, I learnt on a 25ft so that'd be OK too" and now it's to the "I suppose anything up to about 30ft would be alright"
I think I'm just going to have to set a budget (and actually set it, these things have a habit of getting pushed!) and see what the most I can get is. I might even just stick with crewing over the winter as that's going to take most of my sail time anyway.