Drawings
Yes. Lots of them.
Notary
Yes. And a lawyer too most probably (for the making of the land & mortgage register entry).
Planning permission?
Probably not planning permission. But you will almost certainly need permission from the local authorities; and I'd be astounded if you don't also need permission from the building administration, who probably won't want to give permission and certainly don't have to give permission.
Pretty much nothing changes in the apartment,
Gas piping and meter? Cold water pipes and meter? Hot water pipes and meter? Electricity supply and meter?
It seems a better option to split the place if its not too expensive to cut the red tape.
You haven't been in Poland all that long, have you.