1. All K, M, A, F and FA lenses directly. M42 screw mount lenses via adapter, with manual aperture control.
3. Start here...
If you're buying one, watch out for "sticky mirror" syndrome.
The Pentax authorized repair center - CRIS - will still accept LX's, but is starting to warn about parts availability. Eric Hendrickson will still work on LX's too. If you're having an LX repaired, ask whether the shop still has the special goop needed to re-establish full weather sealing when the camera is reassembled.