T tail advantage: If the aircraft is a flying boat, it keeps the tail out of the water.
Disadvantages: Much more difficult to inspect for frost/snow/ice, and clean if required.
More complex elevator and trim control systems, and,
Depending upon aircraft type and configuration, a high tail might be out of the prop wash, which reduces pitch control on the ground (less able for soft field takeoffs).
engines at the tail means they are slightly more protected
Generally yes, though more vulnerable to snow and ice from the top of the fuselage being ingested.