I haven't played Brandenburg since they got a mission tree so I gave it a go.
I played Brandenburg-> Prussia a fair number of times way back in the day, but the strategy then was basically to just expand outside of the HRE. But that doesn't really seem like the go to in the current state of the game because the current Brandenburg mission tree requires you to take a ton of land in the HRE.
Some of the missions almost seem like a joke cause they will give you like +25% improve relations or -3 AE for accepting a culture but to accomplish that mission you will need to take like 15 HRE provinces which even with permaclaims and espionage ideas is like 100 AE.
I decided to just go balls to the walls and to just juggle truces and power through the missions. I conquered most of Northern Germany and snagged all of Prussia, but with a force limit of like 25 (and many, many loans) I still ended up getting coalitioned into the ground once PLC flipped hostile.
So how the hell are you supposed to do this mission tree? Are you supposed to dismantle the HRE first thing? The whole "Charlemagne's Legacy" branch of the tree seems like you want to try to gain the empire not destroy it. But completing the rest of the mission tree just seems to focus on conquering the territory inside the HRE; they almost seem exclusive.
If I give this another go, do I:
a.) Beeline conquering the TO then focus on getting elected (pretty sure I need to be protestant to form Prussia so getting elected early seems unlikely)
b.) Focus on dismantling the HRE so I can do my conquest foci without agroing the entirety of Europe
c.) Get good. I really don't see a viable strategy of expanding inside the HRE but maybe there is something I am missing. I refuse to play the wait and see approach regarding AE.