I use "architectural grade" pine boards for my smaller light fixtures (like those going on a 10 gallon tank)
for larger fixtures, I use plywood, usually birch veneer.
if I bother to paint, i've got Rustoleum "arts and crafts" indoor/outdoor latex in semigloss black and highgloss white
tools; hand saw + mitre box, mitre saw, circular saw, drill, screwdriver, framing square, angle iron, clamps and a recent addition of a small table saw
for your needs, I'd build a canopy that is split 60 / 40 and the front 40 is hinged to fold up and over the back 60, allowing for feeding and simple maintenence. you can buy a cheap under-cabinet light and mount them to the "back half" of the canopy... a pair of 15 watt lights should work well for a fish only tank