As I do not read croatian I can only comment on the aesthetics and I think there is a lot of work to do here.
Depending on how much you are going to invest in the website I would actually suggest hiring a webdesigner to make a complete overhaul of the website. I think it looks quite outdated(as if made in the early 00’s).
There are also many places where you can find good looking and free templates for your website to use. Google is your friend in this.