re 1: Yes, I will add some default text about how to use the site which can be edited before sending. In fact, I need to do more explanation generally but for now I'm going with the simplest implementation.
re 2: I'm currently working on the basis that when someone 'thumbs-up' a place, it means they will attend. I'll re-think that today. Maybe I should have an attend button for those who don't care about the place but wish to attend anyway.
re 3: It is currently possible to add a comment saying '.., .. and .. have been invited' Will that not do the job?
BTW, have you got anything to do with Rhubarb radio at the custard factory in Brum? I'm based in Brum myself ;)