Translation:I know three people who want to learn Czech.
Would it be possible to consider adding "I know of three people who want to learn Czech"? Even though that would be better translated as "Vím o třech lidech, kteří se chtějí naučit česky" I think the meanings are similar enough to be included. I guess when I "know people" I really know them closer than "to know of people" where I know they exist, but I don't really "know them" know them. But my native English speaking husband insists "know people" is the same as "know of people." What do you think?
"S ní" covers the second case as well and sounds less strange. "šťastný z někoho" sounds coloquial to me. Maybe it is possible, but hard to find in the korpus among all the cases of "dnes je z něj/ní šťastný člověk" and similar. And it would be lot of work to add "z" everywhere.