Coco is the fiber of coconut husks, soaked in brine for 1-2 years, then de-salted (cheap stuff needs more rinsing), shredded or chipped, and compressed for sale.
I'd DEFINITELY go with teh Canna Coco because coco sometimes LEACHES OUT potassium and SCAVENGES Calcium, and it's a soilless medium needing just a touch higher pH than hydro, so the Coco line compensates for that in a way the Aqua stuff wouldn't.

I can't really say about the res; it depends on plant size, %RH in the room, temps, light intensity, and feeding habits of that strain. But I think that sounds adequate. Don't worry about altering the pH; not only is that nutrient line well-buffered in range, but concentrated acids and bases change the pH a LOT with just a few drops per gallon, and it is no more difficult to set it in a large res than in a small bucket; arguably, it's easier in a big res because you are less likely to overshoot your target pH.