3 footers take some skill to use because they are so short. Good for stuff under 8 inches though. A good 4 foot one man saw and a standard 2 man 5 and a half footer
should fill out a good cache of firewood saws. double bucking is way faster, so find another good sawyer to help.
There were a bunch of great videos from Warren Miller on filing crosscuts on vimeo a while ago, but they are not up anymore. Those were great, the best videos on the web. There is a
video on youtube by a guy named PATCsawyer who did a little how to. It was a good general intro to filing. There is also a crosscut forum called crosscutsawyer.com, that is probably the only place I know of to really pry some info from. The rest I just kind of picked up here and there.