I have a K40, K9 and MK9. The MK9 is rapidly becoming my primary carry gun. Both my K9 and MK9 are the stainless elite. My K40 is the Black-T model (no longer made) with the elite trigger retrofitted.
I like my Kahrs a lot. Nice guns. I find I'm more accurate with them than with my Glocks. Maintenance? Well, clean it and oil it. Check that the grip screws are tight now and again. I hear that the finish on the economy model isn't that great, so you may want to make sure that you wipe it down with oil weekly if you carry it concealed.
Regarding ammo selection, for practice just about any good FMJ will do. For defensive purposes carry, there are two main 9mm camps: light and fast (Marshal & Sanow) vs. heavy and slow (Facklerites). The former like the Corbon 115 gr +P+. The later seem to like the 147 gr rounds. Pick your poison. Personally, I use Remington 115 gr +P+ (not golden saber). I tried the 124 gr Hydrashok, but that round had way too much muzzle flash in my MK9. Whatever round you choose for defensive purposes, make sure that you put 100-200 rounds through your gun with no malfunctions before you start carrying it.
Jared