Multiplayer is played in sessions similar to Anno or Civilization, with a maximum of 6 players per session (but this number could well increase during Early Access). You can play both cooperatively or competitively in multiplayer. Multiplayer interactions include (For Early Access Release):
Military action is abstracted as Influence Points. You can claim other people's land or vassalize them by using your Influence Points. Likewise, they also defend using Influence Points.
In early prototype versions, I experimented with in-world simulated military units, and it didn't work well. Shifting the game’s economy to build military units broke the flow of the game. Not only that, those who successfully built an army and vassalized others lost their will to rebuild the economy afterward.
By using Influence Points instead the game flows so much better because it works sort of like an auction system. If someone gets taken over (vassalized), they pay vassal tax to their lord, but still keep their town.
In Kingdoms Reborn, players use cards to build and take actions. Every round (two and a half minutes), players get a selection of cards that can be bought and used. There are several reasons the card system is there:
Yes, except for Music and Sound Design, which is created by Alistair Lindsay. Alistair also created the music and audio for Rimworld, Prison Architect, etc. :)