Kind of sounds like two different problems to me.
For the hot hard start. Rohrt is right. The gas today can have a very low boiling temperature. I have a phenolic spacer, carb heat shield and lowered float on mine. If the float is set just a little high a hot engine can expand the gas enough to push it out of the boosters creating a flooded condition. To start, the throttle must be opened to allow more air into the engine. Lower the float level to a little below the sight glass or sight hole and see what happens. Don't lower too much, will mess with the transition. Holley carbs don't like a lot of inlet fuel pressure. Double check fuel pump pressure.
The idle return problem sounds like a sticky linkage. Perhaps a misbehaving choke or choke linkage? Can you replicate the problem with the car sitting in the driveway? Years ago my dad bought a new '69 Belair. The drivers side motor mount separated and would hang the throttle under odd conditions - like my mom driving a bunch of us kids around. Would never hang with dad driving. Finally hung for the service writer after mom bitched at him. He nearly drove dad's new car through the dealership wall. Us kids had a ball that day.