I would also be happy to use it all the time.
"Do you have a lawyer?"
"I don't need one!"
Is prawnik also an advocate in court? Or do you have a separate word for that as we do in Croatian?
It can be. Prawnik is a word for all people whose job is related to law- a Law school teacher, a prosecutor, a judge, a lawyer that can represent people in court, a lawyer who negotiates corporate deals, notary etc. https://pl.wikipedia.org/wiki/Prawnik
"Adwokat" and "Radca prawny" are two kinds of lawyers that can represent people in court, I don't really get the difference, but I think "adwokat" can take all kinds of cases, but has to be self employed.
Also it is customary to call a lawyer "mecenas". https://pl.wikipedia.org/wiki/Mecenas_(prawnik)