Well, there are multiple questions here, lemme break them down.
Did the average Slovene learn Serbo-Croatian in school? If so, did they learn to read in Cyrillic?
Would the average Croat be able to read in Cyrillic? Where would s/he have learned it? Or is it completely foreign to Croats and only familiar to ones that are part-Serb, live in Serbia or studied Russian?
Could the average Serb or Macedonian read Latin? Or only the ones that took French/English/German classes?
Yes, Slovenians learned Serbo-Croatian in schools. I believe it was from fifth grade. Yes they studied cyrillic.
Croats had to learn cyrillic in third grade elementary school.
Serbs had to learn latin script in thrird grade elementary school. Macedonians had to learn latin script in their Serbo-Croatian classes.