How much is 'not enough' or 'too much' will depend on a lot of things, it is best to watch the fish and plants while you try different levels, and different arrangements of the equipment.
Fish from a fast flowing stream will thrive in fast moving water, fish from a lake, or slower moving stream will not like that much water movement. Fish can move to different areas of the tank. If they are always hanging out where the water movement is the strongest, I would add more water movement. If they are always hiding in the slowest moving corners then I would reduce the water movement. Fish that spend time in both areas are telling you the tank is set up just right for them.
I've had to add a nano power head to my 29g to address a dead spot but I've noticed the tetras move to a quiet corner behind the dead spot, where incidentally I'm still seeing pockets of BBA. I've since put the PH on a timer synchronized with the CO2. Are there any problems with this approach?
Nutrient uptake occurs only during photosynthesis, correct?