I don't yet have a microphone so any advice on what might be a good choice would also be appreciated.
As for the connections, Output (R, L/mono) send output signals to an amplifier or DI-Box. Midi In & Out has nothing to do with microphones. In short, this is used for interaction with a PC. In my experience with digital keyboards, the manufacturers will specify a socket for microphone connections and will often provide their own brand of microphone too.
Just looking through the manual, there doesn't appear to be any advice about connecting a microphone - there is a lot of advice supporting the connection of other devices but not microphones. Sound equipment that support the use of microphones have to be able to send some sort of low voltage to the micrphone so that it will work and will usually need speakers capable of coping with voices; Roland, for instance, do make keyboards like this such as the KF-90 but it has a special connection for micorphones. Again, given the mechanics and specialism of microphone use, only certain keyboard models will have this feature.