The kettle doesn't need anything but a spigot, (IMO)
The HLT will probably benefit from a sight glass and thermostat if it's going to on a 3 tier system.
Most in the US seem to use couplers but I use nipples (less connections and It keeps the spigot in closer)
The burner should be fine. I use a <30,000 btu burner.
I'd think twice about using the keg on that turkey fryer frame though.