The answers questions 1. 2.3. 4 . Is to carry out your market research @Prabjot2
This is an international community so we aren't likely to have local knowledge on the Croation market .
you need to start by looking to see if there are STR regulations and if so can you comply with them
decide what sort of Airbnb you want ie city fla/seaside villa then contact local estate agents
carry out research into supply and demand for sort of place you want to buy in location you want to buy it in.