Clausing 5900 as first Lathe?
A 5900 series could be a good first lathe - but, it seems most of these are the variable speed models. If you get one that is variable speed, I'd recommend being very sure that the vari-drive is in good shape. That can be hard for a first time lathe buyer to do, so for that reason, I'd recommend staying away from the vari-speed Clausings in the 5900 series for a first timer.
This lathe was also available as a step pulley model - I'd say go after one of those, maybe add a VFD for single to three phase conversion requirments, and get the bonus of variable speed within the ranges provided by your pulley steps.
If you do get a 5900, and think you're going to want a steady rest, try to get one with the machine, as they're hard to find right now. Interestingly, the 5900 series did seem to get lots of turrets sold with them, so that can be an easy to find part, if that interests you (probably not right away for a first lathe).
Lots of good deals out there right now on lathes that would be good for first timers - I would not overlook Clausing / Cochester, Sheldon, Logan, South Bend, etc. Usually a 10 or 12 inch model might be a good choice (the 5900 series is 12 inch). I'd say get something in as good a shape as you can afford, with as much tooling as you can, hopefully that can pass at least 1-3/8" diameter work through the headstock, and accepts 5C collets. Personally, I think threaded spindle mounts are OK, I like L series (long taper) better than threaded, and D series cam lock spindle noses the best. Try to get a collet setup and a 4 jaw chuck with the machine, if you can.
Don't forget about the tooling, that can easily double or triple your bare machine cost.
Be sure and read Dave Fickens' (sp?) article of
Advice on Buying a Used lathe, and
In (modest) Praise of klunkers. You can find them at his website at:
mermac.com
There's my 2 cents or mabye a tad more....