Hello Sykotron! Welcome to Luna server. The difference between a mayor and baron is only dependent on if the duke helps fund the city or not. A mayor and baron can build all the same things but the mayor would be responsible for all the costs whereas the baron is funded by the duke and is expected to help raise militia. Also by being funded by the duke it is expected to answer call to arms.
If you have specific questions feel free to pm me on the forums or even come chat with myself in discord. I am the hand of the king for Kairos Kingdom and our discord can be found here: https://discord.gg/UqfwhBV
Feel free to come and chat with us as our community is always friendly and willing to help answer questions as well! If you would like to join our kingdom we can certainly chat about that as well!