The kits are about $130 from Champion Toyota, and it's WELL worth it. You have to remember you're even getting a stock metal head gasket in that too.
Replace the front and rear main seals, definitely. Valve cover seals, and cam seals I would change too because it's really quick to do. Keep the valve seals, as you can replace those with a little effort while the motor's in the car, and I wouldn't replace them unless I had a good reason. Head gasket, intake and exhaust gaskets, just keep around incase you pull the motor apart. They're all metal, and should not leak unless messed with.