Only hydraulic gear.

Alternate air is an alternate source of air, it can for example be used during ice, when the normal filter is blocked to have a backup source available.

Alternate air is unfiltered air and should not be used during ground operation because the unfiltered air may contain dust and other contamination.

Only hydraulic gear.

No, it’s not required as the Seneca has a fuel injection system and engine icing normally forms around the venturi of the carb.

Ice can still form in in a fuel injection system in icing conditions, an alternate air source is available in this situation which takes warm air from inside the engine cowling.

Hydraulically driven by 2 electric pumps with a 7 second transit.

Seneca uses MOGAS (red) or AVGAS (Blue)

If you pitch up in a Seneca the speed IAS will decrease, because of the constand speed drive (in the propeller hub).

The propellers want to maintain the original RPM. Therefore the blades will go to a more fine blade setting.

The engine will flood with fuel.

No, you mechanically change a valve that changes the air intake to air that runs past the exhaust manifold and is therefore heated.