Regular antifreeze 50% with water, and a 160* thermostat. 2 1/2 gallons is the right amount, as you want to leave 2 quarts capacity for expansion, otherwise it may just go out the overflow pipe anyway.
Any good detergent oil will work. I only add 4 quarts at changes.
Cut the barbbed portion off a plastic fitting and push it down from the top of the upper hose to hold the thermostat in place. No extra clamp needed, and you want the thermostat as close to the head as possible.