Can't help you with the floatplanes, sorry.

But your second question however.
If I understood you correctly, you are not sure how you're supposed to execute the other approaches, such as ( I wont list all of them)

VOR DME (uses a VOR course for lateral reference and DME for vertical)
LOC DME (Localizer aid, uses the DME for vertical reference)
NDB (where you make use of ADF)
ILS (Standard ILS approach)
D-ILS (same as ILS but you use the DME in lieu of the marker beacons)
RNAV (Can only be flown with equipment able to achieve a certain 'Required Navigation Performance'. Simply put expensive and accurate navigation instruments such as GPS, FMS etc...mostly used by airliners)

Bacially, the flashy names tell you which "tool" you'll use as a reference for the landing. And yes, approach charts for these will help you alot.
Sorry for the brief explanation, but I'm heading for the bed, hopefully some others here can dig deeper into the subject  

The useful thing about the FS9 GPS is that it shows you the approaches. For example, if you select a LOC DME approach to runway x at airport y, it shows you just how to go about flying the approach. With the NAV/GPS switch set to GPS, you can tell the plane to fly the approach for you, or just use the GPS as a visual guide to flying it manually.