If the weather conditions are favorable, there isn't much needed. This would have been a very stable aircraft on its own. If the controls are setup properly in advance of the runway, it will descend and "land" with little input. In all likelihood they used a long approach, strait-in, to an airfield totally cleared of all other traffic. He would have had a strait shot in from many miles away.
The important decision was to keep him following the coastline. A random aircraft over florida land would be a nightmare to locate and deal with on radar, even if the transponder was functional. Keeping him following the coastline would have made the fix much simpler.
Not necessarily, but pilots usually fly those manually because a) they’re the exciting parts b) a certain number of manual takeoffs/landings per year are required to stay certified. (EDIT: This was about airliners, a Cessna is definitely 100% manual!)
As far as I understand, takeoff and landing requires manual control in the same way, or for the same reason, Tesla autopilot requires hands on the wheel. It's mostly liability and trust issues.
