Teawoman,
I think you should go for it! There's a 10 week training series around here that prepares women with very little riding experience for the Cinderella metric century.
It sounds like you're in reasonably good shape with your cross training activities, so you have a head start!
One thing I'm confused about is your mention of the 30k long ride. Um, do you mean that once you start riding with the groups that your long ride for the week will be 30k? If so, then that could be a problem. You would need to find a way to fit in increasingly longer rides to build up to the 100k.
OTOH, if your club's starting point is 30k when you get rolling in April, I think you'll be fine for the metric at the end of July.
-- Melissa
I'll get back on the bike soon, I promise!