When is it better to use global vs local libraries?
When you are on a team, or if you have someone on your team that is specifically in charge of libaries.
How to deal with footprints of the same type (e.g. QFN64) but with
slightly varying dimensions as a result of manufacturer guidelines?
It's really up to you, it also depends on what type of manufacturing you are doing. If you are sending the designs to a high volume manufacturer it's likely that you may need to adjust certain footprints to avoid reflow issues. I think it's best to have a footprint per part on most things. On passives it's probably better to have a footprint for all.
How to keep track of 3D models of the components?
Hopefully the PCBCAD will also track these and goes with part creation, if not then store them in a folder structure on a network drive.
The biggest problems that deals with part\library creation are these:
There needs to be a set of rules that everyone on a team (or one person) follows to make sure the library is consistent in part parameters and mechanical layers as well as other things like part text and how pin 1 notation is represented (this is a short list). The real problem is if one is importing parts from manufactures, as this is quicker but all the parts will be different. So much care will be needed to edit these manufacturer parts/footprints so they share the same look in text and also other mechanical layers such as text on assembly mechanical layers
Part Parameters and BOM generation
Make sure that if parameters such as temp range, votlage, height or other parameters are consistent and checked before adding to library. The manufactures may also require other BOM fields and parameters (such as alternate parts) Make sure these parts are entered correctly into the library
Many PCB teams/companies will track inventory of R&D parts or manufacturing parts, sometimes this means internal part numbers and these need to go into the BOM. It is a real pain to change this later so make sure it is set up correctly from the start. Typically these numbers are listed in the BOM and tracked with each part.
The biggest favor you can do for yourself/team is make sure library creation is setup and you have a process in place for creating parts. Feedback from assemblers/PCB manufactures needs to be rolled back into the part creation process to avoid spending time answering many questions from the CM.