some what new

I wouldn't really recommend using stainless sheet metal. My canopy is wood, and the previous owners cut out a diy reflector. They screwed this into the wood right under the MH retrofit and it almost caught the hood on fire. I think it heats up too much. Or you could prolly get away with cutting it so that not one piece of it touches the MH fittings on the roof. But even still I would buy good lights and don't take short-cuts with lights.

If you are planning on upgrading to a bigger tank I would get a light that you can use on the bigger tank as well.

And hairy mushrooms are really cool, so are some zoas, I like the ones that are the color of peacocks. I don't have corals yet but those 2 items will be my first. And I think they only need PC's. Flourescents are necessary but the hot MH bulbs aren't as important unless you get into the more advanced reef keeping.