If you want to use Heightmaps, use WorldPainter I think.
You can create a WorldPainter map, and populate it with Terraincontrol. Or at least I think that was a thing back then.
As for TC and heightmaps:
Heightmaps are nice, but generating a map completly with an heightmap wont be good. (With Exceptions probably)
The main problem with an heightmap is, where should the Generator know if an height difference should be hard or soft? Are there overhangs? Cliffs?
Also, an heightmap for TC wouldn´t give much precision.
As for MobSpawning, i dont think that has any place in TerrainControl. There are working Plugins for that, and adding that to TC would in my opinion just add stuff for the heck of it.