If you mark you addons .toc to load when the Collections addon is loaded, you don't have to worry about tracking ADDON_LOADED (assuming that's the only addon you're waiting for and your addon isn't doing anything before the collections load, I didn't look).
Code:
## LoadOnDemand: 1
## LoadWith: Blizzard_Collections
You can use a hook like:
Lua Code:
hooksecurefunc(C_MountJournal, "SummonByID", function(mountID)
print("hooked on a feeling ...", mountID)
end)
and because MountOptionsMenu_Init is a standalone function (not a method of C_MountJournal):
Lua Code:
hooksecurefunc("MountOptionsMenu_Init", function(self, level)
print("hooked on a feeling ...", self, level)
end)
This will run your code after the original functions have completed running.