You could just say "This looks cool/interesting." The second part comes off as condescending if you use it too often.

ok

No, he means that certain keys can't be used if it has multiple party members. So he's using shift.

You can use it for more than one person as long as you follow this rule.

THIS MAKES MY LIFE A WHOLE LOT EASIER! Thank you!

How would that work with skills?

Each "class" of skill would have to use the same "type" of timing.