EE here. I agree with most of your guesses as far as layout goes. There are definitely some diodes in there - the devices with a more square aspect ratio and la

EE here. I agree with most of your guesses as far as layout goes. There are definitely some diodes in there - the devices with a more square aspect ratio and large square contacts in the middle. The large power transistors are laid out in multiple "fingers" so current is distributed among them. This both reduces the effective diffusion resistance and alleviates concerns related to electromigration. There are a lot more guard rings than I'm used to seeing, and they're very wide. This is probably to avoid latchup due to the potentially high switching currents, and possibly also for moisture protection ("seal rings" would be on every metal layer in addition to the front end layers). There's one very odd layout structure that has me puzzled. In your "collection of transistors", the top left image has a non-rectangular structure in the middle. I wonder if there was a metal structure there that required a diffusion opening. Or maybe its a BiCMOS BJT?