This is too long to read, but from what I have read I can tell you no one here fasts like this. I don’t know a single person who fasts without fish, or with certain number of meals per they. There are a lot of fasting dishes that are pretty delicious. I eat this way 2-3 times of year, simply because that’s all there is at those three days. Fish, see food in general and vegetables are all good to go. Concerning alcohol it shouldn’t be drunk during the fast, but wine is ok, since it’s blood and all people of course use this loop hole, although many drink everything as usually.
Interesting thing are slavas, if it’s during the fast the dishes should be prepared acording to that, but in my town Syrmians (locals who are here, in Syrmia, for longer time, like centuries) don’t do it, while Bosnians do it. Also in my mother’s birth region (in Bosnia) they fast if slava is on wednesday or friday. The point is no one prepares a modest feast for their slava, it’s as rich as it can be. Restaurants here usually have fast menus, even in our student cafeteria there’s going to be separated fast section on the line.
I could be slightly off on some details. And a fun phrase for the end: Od volje ti k’o Šokcu post. Which means ~it’s optional like the Fast for a Šokac (regionalism for Croat/separate group among Croats/totally separate group, depends on who you ask, they’re Catholic in any case)