Noeski
1.) For an equipment slot like the helmet can I use a single mesh that will be animated/deformed and swap out the sprite or would every single alternate helmet require it's own mesh data?
It is not necessary to have separate mesh data per item, and we would very much recommend against that. In general you might want to only have different meshes if you need to cover very different shapes of helmets which need to be animated differently. E.g. all bow items could share the same mesh. Otherwise you would need to setup vertex weights for each item, leading to a lot of redundant work (and also unnecessary data, increasing file size and load times). Please also have a look at how linked meshes are used in a single project to re-use a single mesh with different attachment images.
I am assuming if I swap out the sprite it would need the exact same dimensions to map properly as well.
Yes, the attachment image needs to be of the same size.
Noeski
2.) Is it possible to export/import slot data or sub data separately? For example if my model file contains 100 helmet slots with mesh data, can I export them individually and then load them so that I don't have a single model with a massive amount of data? I am guessing that this is possible with some data post-processing and modifying the Spine runtime myself, but I'm curious if anyone else has already solved this issue.
I'm not sure I completely understand what you are planning as a setup, since "100 helmet slots with mesh data" sounds a bit like the wrong way. Why do you want to have 100 separate slots and meshes? When using linked meshes, you need all of them to be under a single slot. Having multiple slots only makes sense when the mesh differs, which should be avoided where possible, by e.g. grouping similar items and re-using the same mesh for a group.
In general you can load atlas regions via code from just the atlas assets, without having to manually combine data of multiple skeleton data files (or skeletonData objects). You can check out how to do that in the Spine Examples/OtherExamples/AtlasRegionAttacher example scene, in the used AtlasRegionAttacher script. While this example replaces region attachments, the same applies for mesh attachments. For mesh attachments you can also check out the Spine Examples/Other Examples/Mix and Match and Mix and Match Equip example scenes.
If you need to change more than atlas regions (attachment images) from a separate export, you would need to write your own custom import post-processing script. However, we would not recommend going down that path unless it can be avoided.
This related post might be interesting for you as well:
https://esotericsoftware.com/forum/d/15867-memory-management-of-character-with-many-outfits
Noeski
3.) Along with 2 it would be great to export/import individual animations or groups of animations so that I don't have to load a single massive file with every possible animation and I can load only the specific animations that I will need during runtime.
Could you describe what kind of separate animations you have in mind? Likely you should be able to combine similar items to groups and then only animate each item type once. If you really need to combine animations and meshes from multiple skeleton exports to a single one, you would need to combine them programmatically and adjust referenced indices accordingly. E.g. if the first file contains bone indices from 0-100, and each additional equipment export adds e.g. 3 different new bones, they need to be added to the list of bones and then referenced as 101-103, 104-106, and so on.
