Walking on air = HAPPY
Have stars in his eyes = HAPPY
Be in seventh heaven = HAPPY
Be on cloud nine = HAPPY
Like a dog with two tails = HAPPY
Be over the moon. = HAPPY

Be on top of the earth = also happy😊

would
could
Should

BUT Mould

"Whence" isn't a fancy way of saying "when." It's a formal word that means from which, from where:

Return this evil cat *whence* it came!