Game Design: brainstorming

Things I'm trying to figure out:

• Which system would be better suited for this?
• Will this have a GM or be GMless?
• Will there be only two ghosts or can you have as many ghosts as the number of players?
• How will combat work? What can the players do outside of combat?
• Etc.

A while back, I took notes for this game on Milanote. I have to revisit them and see how much of those I want to use.