Just wanted to confirm if it is valid to use To the Limit after resolving Chewie's free slam. I am 95% sure this works, as even though it doesn't cost an action, it is still considered a special action, aka "=>". Indeed, that was the reasoning behind the ruling that Chewie cannot perform two slams in one turn.

Also, can Chewie perform Slam even if there is no valid target for its effect (for example, in order to play To the Limit)? I'm guessing yes, similar to how 0-0-0 can perform Invasive Procedure even when there is no valid target, just that that part of the effect fizzles out (which in the case of Slam is the whole effect).

I’ve been looking at the using To the Limit after the slam also, and I believe it’s legit. He can’t slam twice because it’s a special action, so it’s a special action.

As for your second question, I’ll just sit back and see what happens.

Yes, it's a consequence of ruling Slam without spending an action to still be a special action.

You can activate an ability even if some or all parts of it end up doing nothing.

Well I would think that since it's already been ruled that even though it's a free action it is a special action (so you can't slam twice), then yes, this should be legit. And it's a great idea really!