Breaking the project up like this isn't making things easy unfortunately. you have to be carful where you extract the second and third archive to, and that there's a duplicate folder in the third one isn't really helping either...
"A meta data file (.meta) exists but its folder 'Assets/1 External assets/ModularSci-FiWeapons' can't be found, and has been created. Empty directories cannot be stored in version control, so it's assumed that the meta data file is for an empty directory in version control. When moving or deleting folders outside of Unity, please ensure that the corresponding .meta file is moved or deleted along with it."
Did I mess up stitching it together?
It seems I actually have to install the latest 2020.3 version of Unity as well, I got compilation errors and dropped into "safe mode"...
"A meta data file (.meta) exists but its folder 'Assets/HoudiniEngineAssetCache' can't be found, and has been created."
... or maybe it's becase one can't use it without having Houdini?