I can't speak for GTO, but I'd imagine Mars transfer would be a little less, maybe ~10kg as the delta-V requirement is a little more. Also lunar transfer would be a bit more because of less delta-V requirements, possibly in the ~20kg range.
Payload is normal taken to mean amount of mass the rocket can lift in default form, so any one off adapters or supporting hardware will need to be subtracted from that number.
This can result in some ambiguity in useful lift, where some systems can provide more services like cooling or power to the lifted satellite, or reduce the vibration/G-loads and ...
Here's a brief list of licenses that we often see clients requiring when putting satellites into orbit:
FAA license for the launch;
FCC license to communicate with the satellite;
NOAA license if you have an imaging payload; and
ITAR or EAR license if you're sharing data with foreign persons.
Here's a link to NASA's CubeSat 101 document, which gives a brief ...