I haven't flown a 200 for about 12 years but I'm more current on the 300 series, both 300 and 350. The first thing we have to remember is that this is aviation and there are thousands of, "I was told once," stories.
I always wait for the ITT to stabilize before going to high idle because I was told once that until the ITT is stable the boundary layer of air that separates the fire from the combustion chamber wall is not fully formed.
I have seen historical data that shows the benefit of alternating starts when it comes to the cost of overhauls. The worry about amperage drop comes from the days of smaller gauge wires being used. The wires used now days is thick enough that amperage drop is negligible.
I've never understood the starting in feather unless you were starting both engines using a GPU so the person disconnecting wouldn't get blown away.
As I understand it, going to high idle prevents the engine from bogging down under the increased load. The start on newer models is still just using the battery until higher n1 it's just that the generator control unit (GCU) is taking care of taking the generator off line and putting it back.
The leaving of the type II prop sync on is perfectly fine airmanship. The old saying is, you turn it on when you buy the plane and turn it off when you sell it.