It's rather lazy of you to post an image (it's small and hard to read even when enlarged) instead of an actual pitch and link to your full portfolio as 4 thumbnails from the same client (when you've allegedly had 20+) doesn't really allow us to gage your artistic range as usually each creator has their own style of thumbnails.

100% customization can only by achieved if you send your clients a fully organized PSD of every thumbnail, not by offering to redo it entirely - that's just additional unpaid work for you. It's great that you offer to fully redo a thumbnail, but it'd be more beneficial to you if you'd only offer changes to the thumbnail you've made for the client as those can be done faster and thus allow you to take on more clients.

You mention packages. Why would a client buy a package instead of paying you per thumbnail, considering there's no benefit to ordering a package as it's the same price with the same perks as if you'd order a single thumbnail?

Good luck with your endeavor!

gRaPhIc DeSiGn Is mY pAsSiOn

fortnite font is this even minecraft related??