You can have full climb power, but if you're pointing down you will still go down.
Exactly what I said - you are pointing down, so your airspeed will be high. Full climb power will require a VERY low nose attitude to be going down, and your airspeed will be off the clocks. Attitude IS airspeed.
If you set constant power for level flight you can still climb and descend just using the cyclic.
Still true. Raise the nose, your airspeed will decrease as you climb at a reducing rate. Lower the nose to descend, and your airspeed will increase.
For any airspeed, there is one power setting that gives zero ROD = level flight. But for one power setting, there are usually 2 airspeeds for level flight. White man magic, ain't it?