I know it's a major drag to get a bunch of negative posts on your first tank thread.. I think most of us probably overstocked our first tanks, and had a mishmash of fish that are sub-optimal. I think you deserve a little slack for that at least. But frankly, aside from the issue of water volume/water changes, you have some fish that shouldn't be alone in a tank that size.
Rams - let alone an angel ram - for instance, generally shouldn't be permanently in a tank smaller than about 20 gallons. They need room to form a territory, and while it might do ok on the short term, it's not what the fish deserves. That many Corys probably need about 20 gallons to be comfortable too.. then you add CPDs and killies.. all of which would like to be in more space than 5 gallons. You have the aquarium equivalent of 23 people living in a 500 sq ft apartment. Is it possible, yes.. but is it going to be pleasant for the inhabitants? No.
Other than that, a pretty decent first tank.