Tobias said:
He recommended 14k white gold.
Why on Earth?
I might have understood a price argument if he proposed Palladium - another naturally white metal, not the yellowing white gold... At least if the option was for gray gold (the Palladium-based white gold alloy that does not yellow) or at least 18kt.
Apparently, you are looking for a very rare, precious gem and a custom made setting. I would imagine that the cost of the metal is... immaterial compared to the rest.
My main concern about the ring would be wear - pearls are not 24/7 gems (if any is, but that's another matter). They re very tough (ever tried to
break a pearl?) but easily scratched, tainted by household and makeup chemicals. Meaning - this ring will be wearable, of course, but the design of the setting and the wearer should take care of the pearl.
Short of hiring a structure engineer for the project, classics should work; pearl rings have been around for centuries with the few elegant staple designs never changing very much. Not that you shouldn't get as creative as you want. Loved
THIS at PP, but the tall ring does not inspire frequent wear (not that there is any contradiction with the choice of such a pearl! that one will likely get pampered big time); but would think
THIS is the protective choice especially because the respective black pearl is not all that large and the setting hugs it allot....but the old way of building a
barrier of little stones between pearl and potential bumps is no worse. And if wear was no problem... minimalist rings that make the pearls appear to float over the hand are great

Here's
proof 
but... I wasn't thinking of e-rings then, for sure.
Anyway, 'guess you realized by now I am a... jewelry campaigner?

Everything is simply an opinion, of course.
It is nice to hear about a project like this; 'natural black pearl' sounds absolutely irresistible
Best of luck!