Hi @Natschz . Good questions.
Regarding personal vs. professional pricing tiers -
The same Standard License usage rules apply to both Personal and Professional pricing tiers. They’re pricing tiers, not different license types, which is the key thing here. So, to your example, whether you got something under the Personal pricing tier or the Professional pricing tier, you would be able to retarget animations either way (assuming it’s the sort of product that would allow that, of course 
).
These pricing tiers were intended to give both buyers and sellers flexibility in how they offer and acquire assets. The needs and financial resources of a student or 3-person studio are very different from the needs and financial resources of a larger, 100+ person studio. The pricing tiers were intended to address that and ensure that everybody can find something that suits their needs.
Regarding referenced vs. source assets -
Source assets are assets that you get the files for (e.g., OBJ, UASSET, FBX). You can download them and you can edit them. They can be used in a variety of digital content creation tools.
Referenced assets are assets that refer back to a static source asset. They cannot be downloaded to your drive and the source file being referenced cannot be modified. Currently, referenced assets are only supported in Unreal Editor for Fortnite (UEFN).