#1 Lite-c is more powerful and fexable then c-script imho, C-sript is dead and I don't expect it to be around for to many more versions of 3dgs. If you are just learning 3dgs scripting I'd learn Lite-C.

#2 hieght map import into the include modeler (med) can be saved as useable .hmp file for 3dgs it's pritty simple. just check the scaling as MED trys always to down scale objects imported.( don't know Y this is).

#3 I perfer to use 3dsmax to build my level in and then import it into WED. Just a perferance.

#4 there are a few project that have been done with the engine that are simuler to yours

My two Cents
Malice