Sorry to be late getting to this one... Yep, I've been running the antique sewing machine users site and email list for about 12 years now... close to 2000 members... all sewing on antique treadles and hand cranks.
Get an old all iron, including the gears, straight stitch machine. Don't mess around with new stuff with fancy stitches, not enough strength and depth of stitch and wear out fast. Most of the old iron machines will handle light leather and canvas, but not heavy leather. Sometimes you can get lucky and find an old heavier industrial machine. I just sold one last night... 45# Singer 31-20. Have to pack and ship it tomorrow.
Anybody interested in old time stuff and the outdoors is missing a lot of fun if they don't sew. I've sewn projects on machines as much as 125 years old!
Sewing is really no different than shop work. You have to plan a project, cut the pieces and them join them. Learning to set up and use a straight stitch sewing machine is really no different than learning to set up and use any other shop machine, like a table or radial arm saw... a little study, a little practice and start with simple stuff.
These old machines are great for wool hunting shirts, capotes, all kinds of small gimmicks, etc. The treadles are definitely preferable to electric, but it's the machine head that makes the difference. Look for an old Singer Model 15, or one of the common 1950's/1960's straight stitch Japanese clone copies of that machine. These turn up a lot at thrift stores, garage sales and Craig's list. Often you can find an electric machine and later a treadle and fit the two together.
There are complete instructions on overhauling and restoring the old machines on the Treadle On web site:
www.treadleon.net There are sections called "The Sewing Machine Shop" - for machine work; the Wood Shop - for restoring treadles, and much, much more. It's a huge site. I know... I built every page!
Here's a sample of a typical project that crosses from my sewing machine interest to archery... a roll up case for a two piece longbow:
http://oldpharttsarchery.com/buildingstuff/case/case.html Yesterday and today I sewed up two padded recurve cases with full length zippers... not that was a lot tougher project than most, due to the padding and zipper.
Like I said, a lot of fun to be had in the winter when you can't get out. You can contact me for advice if you get serious.