The Tome's support files are not compatible with CC3, but I understand that most of the tutorials and such within it are still very useful. I don't have it, myself; I'm going to wait for the update, so don't take what I say about that subject as gospel.

Fractal Terrains is very nice if you need worlds completely from scratch or you want heightmap data. If you already have an idea of how you want your world to look, then I'd skip it for now.

City Designer is a wonderful product, but I think you might actually want to look at Dungeon Designer first--that's where you're going to get a lot of help for encounter-level maps.

Also, take a look at the Cartographers' Annual. Each month has a nice tutorial that produces a new and significantly different style. Most of them are overland maps with CC3 alone, but there are also some months with further support for Profantasy's other products.