I wanna go all the way with the Minutemen but I read that there is late mission where you destroy the Predwyn if the BoS is angry at you. Is there a way to do the finale with the Minutemen but not kill off the BoS? I really don't see them as bad guys.

I think the main thing is to go deep into their quests enough that they don't see you as a threat. Basically, you need to earn Maxson's thrust, and it should be enough once you finish Danse's personal quest since you get promoted to Paladin.

dont let that happen

Cool. Once I finish fortifying the Castle I'll go join the BoS

I see, I always do their quests since I like Danse, so it never occurs to me. It's not like there's a downside to doing BoS quests anyway, you get a lot of power armor components, paints, and 2 nifty power armors in the game.