How To organize Taxonomy Vocabulary with overlapping terms - Content Display pages and future proofing
I'd not use a taxonomy at all for implementing what you're asking for. Instead I'd use the Entity Reference module and add an entity reference field like so (in the order specified):


create an extra content type (say) "Artist".
create a node for each Artist you ever want to be able to reference in any of those 4 fields.
make each of your 4 fields an entity reference field.


That's all you'd need.

If I may say, this would still be a solution that could work if some day you have hundreds (thousands?) of Artists. If however you'd use your option 1, or option 2 (using vocabularies), do you think that would still be "usable" (practical)?

However, you may then also want to enable the Inline Entity Form module which, as mentioned on its project page, "provides a widget for inline management (creation, modification, removal) of referenced entities". 

More info

Have a look at the answers to these questions for some related topics:


What is the feasibility of using Entity Reference instead of Taxonomy?
Entity reference vs. taxonomy.
Convert taxonomy to entity reference.
Article about Inline Entity Form.


PS: this could work for either D7 or D8.