ACTIVATING MAGIC ITEM
I'd say judgement call for GM. A wand would require to be used like a weapon, for example. But a ring or other worn item would probably be no problem.
RETRIEVE SPELL COMPONENT
I'm sure this is in the rulebook somewhere. You have almost no chance of spell success in a grapple anyway - why bother.
USE OPPONENT'S WEAPON
I'd probably allow using the opponents own weapon against them, as long as it's light and not a natural weapon.
The pinner can still speak.
Of course you can disarm in a grapple - once you've maintained the grapple that would be the attack.
Ancient red dragon has a CMD of 52. Even a level 20 fighter would be hard pressed to make that check. I would probably disallow this in regular combat, and allow various skill checks for doing something cinematic (such as jumping down onto a flying dragon's back from whatever.)
Larger dragons are literally big enough to pick up player characters however - you'd probably find they'd pick up 4 medium size creatures and drop them from 100 feet up all the time. There's practically nothing they can do about it.