Wow this guide is bs. I did everything according to the Rifa route and got Aerith. Thanks for nothing!

I can't seem to find a way to progress in Chapter 3 without doing at least one side quest. Anyone have an answer to that?

The amount of quests you do is the most important especially if you are trying for Barret. Complete zero quests for both 3 and 8 then do the negatives for Aerith and Tifa.

Having all quests in chapters 3 or 8 completed or not has an effect too

There is also the point after falling through Corneo's floor where cloud chooses to talk to one of either girl first, but I suspect that attempting to walk away from both would affect Barrett's alignment.