I'd prefer Sanji and Zoro to not gain Devil Fruits, too. If they did, I'd want Zoro to get Orochi's Fruit so he could do 8-blades with the heads, and Sanji get Marco's.
I think Blackbeard went from Whole Cake Island to get the Road Ponyglyph, to Sphinx to get Whitebeard and Ace's corpse and resurrect them, then get Zou's Ponyglyph (since it's outside Wano), then hit up Wano to get the Road Ponyglyph, Pluton, and Sukiyaki, a translator.
Based off a map that was released, it looks like the Straw Hats are sailing to Sphinx. I think they'll run into Blackbeard on the way there, or chase after him after finding out what he's been doing to their friends. This allows Blackbeard to gain a bunch of Ponyglyphs, and Pluton. I also think BB already picked up Shirahoshi, too. So, Marco and Sabo would fight Blackbeard sometime around then.