yet ="used to introduce a statement that adds something to a previous statement and usually contrasts with it in some way"?
"Jednak nie jestem artystą"
(also : ale, lecz, jednakże)
lecz= ale English but
or Lecz! = Heal!- singular imperative from leczyć= cure, teat, heal
To my understanding, putting "Still" at the beginning changes the meaning to something like "However".
The Polish sentence is like "I practice a lot but I still don't think I earned the right to call myself an artist".
Is JESZCZE only used with negatives, or could you say CZY ON JEST JESZCZE ARTYSTA "is he an artist yet?"?
I think "Czy on jest jeszcze artystą?" would be "Is he still an artist?" - it's hard to show it on the example of an artist, so let's go with president: "Czy on jest jeszcze prezydentem?" = "Is he still the president?"
If I understand your English sentence correctly ('yet' was always a bit confusing to me), it should be "Czy on już jest artystą?" - it means that I ask if the moment when "he" could call himself an artist has already come.