I'll answer the second question first.
In the Map Settings screen, after selecting a hex grid, there's a checkbox labeled "Snap to hex" that you need to enable. I think that's the step you're missing. It sounds like you've had it set to snap to a square grid, which you sometimes want, if you're making a map with tiles and tile overlays rather than hex-shaped assets.
As for wilderness mapping, here's a list of Add-Ons that can help:
Most of
Gabriel Pickard's Add-Ons have a grass tile or texture that might help as a background to place vegetation on.
The pack that would have been
ideal as a basis for most wilderness maps hasn't actually been released yet. You can see a preview of it
here. Alas, the Kickstarter campaign to fund it failed miserably. I'm hoping to self-publish it after MapForge v1.1 is released.