There's a lot of good discussions in the operating/routing sub-forum. I'd suggest going through some of the threads in there.
From what I understand, it's hard to do a 50/50 split these days. Some folks have said 60/40 in favor of the operator.
For the most part, no. Small rooms like the ones you find in walmart or theaters *might* have some rent involved.
You need to get a county tax permit for each machine. It's usually a yearly fee. Some counties it's reasonable, but others still have their laws on the books from when coin-op was hot, and it can be quite expensive.
Sometimes. It's probably best to have at least a 1 page agreement written up stating who is responsible for what, and what the split is.
Always the operator. You don't want unknowledgeable staff messing with your game, and staff don't typically have time to mess with it anyway. A lot of times when there's a problem, they'll just turn the game off, sometimes without notifying you, so you will have to check on the game constantly.
YES. And get insurance. DO NOT take the owner's word that you will be included under the insurance for the establishment. If the situation arises that you actually need to make a claim, you'll find that you won't actually be covered.
Operating costs for routing can get expensive, which is why most people don't bother with it for just one or two games. You really need a larger fleet to make it worthwhile.
LLC setup; possibly hiring a lawyer to help; public notice costs; registered agent costs (if you don't want to use your home address), additional permits/licenses depending on your state/county.
Income tax on earnings
County game tax permit; there might also be additional permits and licenses needed, depending on your state/county.
Possibly hiring a CPA to help with tax accounting