This design is very similar to what I did. Same exact cooler from Home Depot.
I took the really easy route and just used a spigot assembly from a hot water heater. It had all the flanges, interior nipple, and valve already built in. In total I bought 4 parts: The hot water heat spigot, the cooler, a SS gas heater line for a braided mesh and a nipple to go on the end of the water spigot.
I spent more though trying to keep it simple. Maybe an extra $5. Love the simplicity of the design.
I like your design and the right up. Good job.