I disagree in part, Engines. Yes, the 27mm Mauser is a compromise, but I would say 20mm with a much higher rate of fire is the air-to-air weapon of choice while the 30mm in all its guises is more effective against harder ground targets.
I always thought it was a mistake going with the hard driving band for the Mauser round, but apart from that it is very good at what it does.
Typhoon, yes, what you think is correct. In simple terms, anything you bolt on the outside of F-35 spoils the invisibility and further decreases range. But the brains believe (or convinced the bean counters) that's OK after day one of the war. The weapons bays aren't that big so to carry a decent mix of weapons in decent numbers, we'll have to make it look more like a loaded F-16.