Here is some more progress on the forest base.

I infused the leaves with some wood hardener, to give them a bit of protection from any other wetting agent that I will use (varnish, paint, etc), so that they don't curl up too much.

Then I also added more rocks and leaf litter, and squared up the base a bit.

I plan to add some more ferns, and a lot of moss, after painting the tree trunk. I don't think I will repaint the leaves or the leaf litter, since they already have beautiful shades of green and browns.