I think your calipers will reach, but if your rear caliper doesn't reach there is enough meat in them that you can just take a file and extend the slot a little more.

Freewheel vs. freehub, see here: http://www.sheldonbrown.com/free-k7.html

I like Panaracer Pasela tires for general riding. They're cheap enough, feel nice to ride on, and come in 27" too.