Let me begin by saying that I freaking love this piece. I never heard the original recording by Art Tatum, but got exposed to it after hearing it on Yuja Wang's new album.
When it comes to difficulty, I think it's monstrous. Firstly if you've been purely classically trained (which is my case), and haven't had much exposure to Jazz/Improv/Ragtime piano, this piece can get extremely awkward for you. You mention working on Chopin Op 10. No. 3; these two pieces entail completely different difficulties from completely different eras of music...so if you're thinking your mastery of the Chopin will assist in "Tea For Two"....i don't think it will exactly translate to that so much.
First look to easier Joplin pieces to get you accustomed to the musical style....then I guess you can progress your way up, after some familiarity with the styles idioms.
Also remember that Art Tatum was a RIDICULOUS pianist, and he may have simply transcribed something he was improvising...so there is no way this will be a simple task!