I know nothing about being an operator. Even if the bar owner is a friend? Cover your own rear. I've learned this from other business's. You kind of have to weigh that out too, depending on the value of the machines and a possible injury. At the very least protect yourself from someone claiming an injury. I've learned to never rely on someone else saying they will protect you. Friend or not get everything in writing. Not to be the negative guy. But think of the worst case scenario and plan on it! If it comes out better than that? Then your all good!
Taxes? A while back you didn't even need a tax ID anymore for some stuff you just used your social. You may want to check into that. I really don't remember all the ins and outs of that.
I'm sure there are many directions you can go.