Hi, I'd like to know:

1) where is the Tree Collection?
2) There is a way to regulate the blending of the sculpt and terrain painting brushes. The brush is too hard
3) Can I upload an animated FBX model?
4) Can I upload an external character?

Thanx

1) Whatever models are currently with MAX you can use. Else, you currently use what trees are with the current bios when generating terrains. They may create more vegetations, including trees down the road, but I can't say (as I don't work for them). But MAX is currently in alpha.
2) They are still working on this and apparently, when they are finished with the terrain, there will be smoother transitions between terrain textures. Remember, this is still alpha software.
3) Yes, you can. You import animated models the very same way you import static models into MAX.
4) You can import a character model the same way (see my answer to 3).