Neumann's KM86 is one of the most sought-after small diaphragm condenser mics with three pickup patterns (cardioid, omni, figure eight). Long discontinued, it still enjoys great popularity among professional studio owners and users because of its natural, unhyped response and musicality.
The mic needs no maintenance, unless you find that its sound is compromised (hum, irregular discharge or other noises, low output). Make sure you always keep the mic in a plastic bag when not in use (even a produce bag will do).
Any phantom power supply putting out nominally 48-52VDC will work, and you cannot destroy any parts of this mic by just plugging in. But make sure that the output of the AKG phantom box (you did not mention the model) is DC-free, i.e. the DC portion that rides on the same conductors as the audio (AC) has been filtered out.
You will know whether the supply is doing its job as a stand-alone the moment you plug it in: if only hum can be heard, you will need a DC decoupler of some kind.
