More to add... you don't want them too close to each other, so that's why I say the spacing looks good. You don't want the first too close to the wall, so it can have space to grow, unless you want to train it up or whatever. The places to feed seem fine, although I'm not sure you need the second set as the first will trickle down, but more can't hurt. I guess my only thought with having watering tubes going to 4 different places is the pressure being low. I'm guessing you are just going to use the waterfall effect to get oxygen to the water. If you are going to use an airpump and stone, then no worries. But if you are not, then you have to remember that the only way oxygen is getting dissolved into the water is when you spray it into the tubes, and when it falls back to the rez. Your fall isn't that big so it won't be making too much oxygen, so really I'd be looking to spray it in pretty good with the feeding tubes or whatever you want to call them.
Hope that makes sense.