I didn't quite understand what you meant by the second point; did you want something that pauses the wave duration so you can prepare for the next wave, or just a button to move on to the next wave more quickly?
The problem: waiting for next wave is too long.
Solution: make less time between waves (e.g. 10 sec)
Issue: 10sec is not enough to make some changes by player, thus it could be useful 'Pause' button to stop 10sec timer - make changes - unpause to start new wave.
or just a button "Start new wave", yes u r right.