[Fyron]

You can easily combine Deathstalker's Mount Mod, FQM and one of those other mods, as they all mod different things. DMM you need just the CompEnhancement.txt file. For FQM there are detailed instructions in its Help folder for how to combine it with other mods.

As for Planetary Assault and Dark Horse, I am not familiar with them. What you will want to do is figure out which one mods the game more heavily, and use that one as your base. Create a new mod folder to contain your merged mod. Copy the base mod into it. Merge DMM's single file into it (overwriting the mount file should be fine). Merge FQM into the mod. Then, go through the other mod and compare differences in the files, adding and changing what you want to.