Mazeppa is a great piece, but to make it sound like it should sound is quite hard I think. Playing the first two pages up to speed is quite nice already though, keep up the good work.
I also use the 4-2, 4-2 fingering for the thirds. You can really add power if you play the thirds with 4-2, 4-2 fingering imo.
People who think that Mazeppa is a "quite easy" piece are completely wrong with that. This piece is challenging and quite difficult to memorize. Though, it's fun to play and that's what piano playing is all about, right?
If you finishied this piece, I'd love to hear a recording from you of it in the audition room!