Re: More than 6 Pokemon on hand?
Indeed, if he has an extra Pokemon at hand (from the usual six), the button will glow red, making it unusable. This must be the universe's way of saying that you can't have more than six in hand. However, Ash does rotate his Pokemon around, with reserves located at Juniper's lab (like how Oak keeps all of Ash's older Pokemon).
Interestingly, in the Kanto saga, when he caught Krabby (the seventh at hand), the ball disappears from it like it teleports away on its own, which was initially how the universe show you can't have more than six at hand. I think I recall Gary having a sack of Pokemon and claiming to have caught Pokemon in all of them, so I suppose the system is inconsistent. It's inconsistent between the times, I know, but the newer portrayals are generally more consistent, because the older times were weirder (like how Dragonite at the Orange Islands got to use more than four attacks).
Thanks for reading.