I'm in the process of "rebuilding" a Logan 200, so I can answer a few of your questions. The bearings in a Logan 200 are ball bearings, not roller bearings. Unlike many lathes, they are not adjustable: the preload
is "built in" to the bearings. The front bearing is a double row bearing that, while not available from bearing houses, is still available from Logan. (I just bought bearings for mine.) This brings up a good
point: the Logan is one of the easier older American lathes to support. Because they were build in large numbers, there are lots of eBay parts available, and parts are still available from Logan as well. (
http://www.lathe.com). In general, Logans are considered a better lathe than an Atlas: more robust, better ways etc. joebiplane's suggestion to find an 820 is a good one since the 200 didn't
have a quick change gear box, but really you should focus on finding a lathe in the best condition you can find, with as much tooling as possible. All these old machines have wear, especially to the bed,
and of course many were abused. Changing wear items like bushings, bearings, belts etc. can always be done, but avoiding a completely worn out machine will save you headaches later. You may want
to learn a bit about evaluating a lathe, and then take the time to find a good one. My machine is in pretty good shape, and I didn't overpay for it, but I've still spent more on parts and tooling than
I spent buying it, and I'm not done yet.
I would start by checking the FAQ on Logan's website, and check out the
"LOGAN ENGINEERING CO. & LOGAN WARDS " discussions elsewhere
on this site. LOTS of useful information that will help you make a good
choice.