First off, how did you go about fixing this mess?
I enabled all mods, waited for OXCE to give me an error, fixed the error, restarted OXCE and waited for another error. Rinse and repeat until fully fixed.
Whole process took about 20 minutes, maybe 30.
Granted, most the mods work, but some don't and additionally they interact. The Hangar mod for example doesn't work stand-alone (at least it crashed when i tried it since some definitions were missing).
As you said, it's a mess, the mods are not standalone... I didn't fix that.
I assume the original authors made them standalone, but Thirsk probably messed with them and made them the way they are (sorry if not true).
Secondly, how did you fix the missing item definitions in MIB/Equal Terms? They started out with the grendae launcher and kind of went from there.
They were defined in other mods, I fixed the other mods (many just by adding metadata.yml) and that fixed it.
Thirdly, did you fix the sprite numbers in the weapons addons just for the heck of it or are large sprite numbers inherently bad?
I fixed sprite numbers on some smaller mods, especially Unconventional Weapons, which was using indices over 100000 (SadFace).
It is inherently bad and it wastes a lot of memory.
If you have a mod with one sprite and you give it index 100000, OpenXcom will actually allocate all the 100000 slots even if they are not used.
DON'T DO THAT.
Every small, medium and large mod should only use indices below 1000.
Huge mods (e.g. piratez) have the option to allocate more than 1000... but even piratez for example doesn't use more than 4000 today I think.
I didn't fix Equal Terms indices, because there were lot of them.
I just increased the reserved space for this mod to 55000, which is a terrible waste of space, but I was not in a mood to play with numbers.
And the author should fix it anyway, not me, so that everybody can benefit from it.