I understand your dilemma. I recently came to the same conclusion, that I wanted to focus on my art instead of the other things. I found that you can change your name on Instagram really easy. Just go to “edit profile” and change your name under “username”. At least, it worked for me. Though I understand your conflict with branding since you’ve used that name on other sites.
As for the followers… unfortunately, I have very few right now, so I didn’t worry too much about changing what I wanted to do. Plus, my account was already diverse. You, on the other hand, have quite a following, so changing the focus of your account from cards to art will have a bigger impact. You might lose quite a few followers, but then again, you might keep a lot of them. Whereas if you start from scratch you will lose all of them.
Anyway, that’s my two cents. I hope what I said makes sense.