Run a TOPs tournament. My best one paid out over $400. Software is already there. Charge $2 for a tournament game with $1 of that going towards the prize pool. Once started, the display shows details about the tournament including prize pool and current top scores. I ran mine for around a month each and always finished them on a weekend so people could get paid that day. You'll need a tournament button, if you don't already have one. Marco sells them.
Many cities now have all their rules listed online. Use search terms like amusement, video games and of course pinball. Rules can vary greatly from city to city and lots of large cities have no rules at all regarding pinball machines and video games. Always best to check first. Some cities have quirky rules leftover from the 80's when video games went nuts. My city requires a police background check if you operate 10 or more games at a single location, which I never did.
I never considered getting insurance when I operated pins because in the 50 years I've been playing (and 10 years of operating), I've never seen or heard of anyone getting hurt by a pinball machine. The businesses I put my games in did have insurance.