How would you ADC guys go about sealing up these areas?

Depends what you're trying to keep out. Bats aren't chewers, so foam or silicone caulking works. If mice, I would go with metal flashing or Xcluder. Any kind of squirrels would need flashing or hardware cloth. Same for sparrows and starlings.

A little bit of everything. The first picture would be birds and flying squirrels. The other (2) pictures are mainly mice.

Metal is always great, but if not an option, I would use xcluder fabric and use a good caulk. Sashco slab or one of the mor-flexx colors might be a good match.

Stay away from silicone. It will be absorbed by the wood and will be a problem.

Is that a chimney? If so, take fire code into consideration. You don’t want the finger pointed at you if a house catches on fire.