Just an update, for anyone who's following this thread, I've decided on the tank and bars, but I can't get her started... (see other thread!) I still need to source an 18" front wheel, but with the tank decided upon, I can plan out the fabrication of the seat and try to hide as much gubbins underneath it as possible...
I really want to make sure it's running right at every stage of the build though, so I know that if suddenly it's NOT running, the cause is whatever I've JUST been messing with!