Voodoo/Vodou/Hoodoo, along with related practices like Santeria & Candomble, are BIG parts of Creole & Afro-Caribbean culture. Are there enough practitioners to make an impact on ticket sales? I don't know, but I doubt Marvel Studios wants to risk it.
He can, by invoking the loa. This is often accompanied by smoke and the sound of drums.
Regarding his look, I rather like the outfit he had at the end of Avengers #690:
Maybe not the big earrings, tho.
As for his backstory, given that Jericho is canonically an accredited psychologist, I'd swipe an idea Priest used for Shadowman back in the Acclaim days, and make him a late-night jazz DJ in New Orleans who uses "Doctor Voodoo" as his nom du micro.
It was a great bit, and it always annoyed me that the publisher didn't do more with it.
https://web.archive.org/web/20020817.../shadowman.htm