I think I finally did it, thanks to the incredibly helpful tips in here. It's still not perfect but I think this is as far as I'll come in this ME.
I know this isn't unheard of with Bayern especially, but defeating Barca while trying to emulate Pep's crazy ideas will always be a highlight.
It took a lot of time, but eventually I was able to figure out a tactic that gave me what I needed and wanted without having too many obvious flaws. This tactic will struggle against teams that park the bus because the 'Cross from Byline' PI is still busted and the Full Backs will just launch cross after cross from deep but that's not something I can fix as a player without SI adressing that in the ME. For now, I'm very happy and I just hope FM20 adresses the final few quirks that keep tactics like these from fully blossoming.
Cheers to everyone who shared their thoughts in here!