Looks good, but I'd say from personal experience that you may want to reposition those stones a little so you can get to all the glass for cleaning. The exact clearance will depend on the type of scraper you're using but they all need some gap and it looks like things might be a little tight on the sides. It really bugs me that I have a patch of algae on my glass that neither my scraper nor my snails can get to.
I have the smallest Eheim canister filter for my 12 inch cube. Its still way too big, but I don't think it hurts.
I can seem to grow all the usual beginner plants okay using Excel as a carbon source, but the carpeting plants all slowly die on me. Maybe you need C02 for them, but I can't personally justify the kit for a single 12 inch cube.