Lots of people on trials forums say to get something small and >250 will be a handful. I came from an mx/enduro/stuntriding background and my first trials bike was a 2.9 Sherco. I never had problems with throttle or clutch control. As long as you aren't a ham-fisted goon you shouldn't have a problem. I think it probably comes from old guys who hardly use the clutch. As long as you keep one finger on it and pull it in as soon as you get a bit out of shape you should be fine.
As for bikes, I went for the newest I could and think you both should too. I couldn't see condition because I bought it over the internet. After a few years when I'd tried some and knew what I liked and wanted I bought a Honda-Montesa 4rt. Was more expensive than other bikes the same age but they hold their value if I want to sell it; very reliable, and hasn't changed much over the years so plenty of parts etc.
Can't help with where to buy one other than rypusa.com has a few used bikes and Ryan is a good dude. Also, his training dvds are pretty much the best out there.
You could try to find clubs near you but I have no idea how.