In my view, .090" to .010" above the 12th fret would be considered medium action on a tenor uke. .080" would be low and .120" would be high. Anything higher or lower would be unplayable for most players.
aAnd for the nut slots genberally if you press the second fret the string should just miss the first fret and can actually in theory if your neck is flat and straight almost touch the top of the first fret...