You need liability insurance, your own, not the convention's.
You need license stickers for the city/county (yes, even if they are set on free, most cities consider them Coin-Op, and inspectors love to be pricks with pinball/slots). A few cities will let you run a screw into the coin slots to disable them, but you better call and get any variance IN WRITING. If the city or county confiscates your games, you will never get them back, unless you buy them back at auction.
Some cities are so crazy about coin-op that distributors sell totally blank coin doors. They would not make and stock such an item unless there was a real need...
The deductible for damage to your games will probably be $1500, so make sure you are ready to accept any peeled decals, bent shooter rods, or coming back Sunday and finding your games are simply gone; stolen by one of the vendors. Vendors have the handtrucks and tools needed to steal pins - they are like carnies but they have teeth.
I'd charge $3000 to bring three SS pins to the show for the entire weekend.