I have heard good things about Litchi, though I haven’t tried it myself.
For forest, especially over varied terrain, you will need lots of overlap, but also a fair amount of variation in flight angle. In the docs, we document how to, in a very robust way, ensure perfect camera calibration:
https://docs.opendronemap.org/tutorials.html#calibrating-the-camera
I need to rewrite this section, as there are easier ways to achieve good camera calibration. But this description of how to fly is very useful for forested landscapes, specifically performing a pair of cross-grids separated by 20°, ideally with a 5° forward facing camera.
Crossgrid overlap percentages can be lower than parallel flights. To get good 3D results, you will require 68% overlap and sidelap for an equivalent 83% overlap and sidelap.
As you have varied terrain, you may want each sub-flight (of the 8 subflights) to have 69 or 70% overlap / sidelap for overlap in excess of 83%
Doing so will give you really a really nice surface model and accurate orthophotos:
