Making maps doesnt require much PC power. Its not even too complicated.
Whats complicated is the Terrain editor and his quirks. But once youve come to understand what it likes and whats a no-do, all it takes is patience and lots of time.
As for the elevations: Ive searched the globus for some goodlooking geo-maps and converted them to terrain files. Do a search in terrain forum, theres different programs you can use.
Youll just have to check the terrain and level the water tiles.