um... not sure it is a good idea to hang the light inside of your canopy if it is only 10".
few things you will need to consider,
1)each fixture comes with 2 power cord from what I believe, you will need enough space to get 4 cords in your canopy.
2)At 32" deep, the fixture gives about 125 PAR which concern me a bit as my 72w fixture when blue and white are on (60W), it provides about 110 PAR and that is 35" deep. That can mean few possibility, either it is not running at full power or the LED
being used is not at high quality.
3)I saw these fixtures before, there should be fan on top. So when you hang them in your canopy, you will need to give at least 3-5 inches for the hot ait to get out, or you will decrease its life span.
To answer your question about wat is too much and wat is too little.
I think the following guideline is pretty easy to tell you wat you need to know when looking at a PAR reading.
(Acropora) require 200 ~ 550
(Montipora for example),Clam and LPS
150 ~ 250
Softies are 50~150
If you run over 300 PAR for softies, you are going to kill them.
if you are running over 500 PAR for SPS
then they could get sun burn when you first introduce it.
I hope this answers some of your questions