First thing, welcome to Tropical Fish Keeping forum.
Tackling the algae first, it depends upon the type of algae; most so-called algae-eating fish are particular as to what they will and won't eat. Also, some can get quite large and cause other issues. Live plants will help control algae, but the light has to be the limiting factor to plant growth, not nutrients (including CO2). It would help to know the light you now have, as it may be a simple matter of reducing the duration if the intensity is not greater than what the plants require. I would look into the light issue before suggesting more fish.
To the fish. First, we have profiles, under the second tab from the left in the blue bar across the top of the page. If the name (common or scientific) is used the same in a post as in the profile it will shade, example Black Neon, and you can click the shaded name for the profile. Data on numbers, compatibility, tank sizes, water parameters, etc are included in the profiles.
Increasing the tetra is good; shoaling fish are always better in larger groups. But the angelfish and gourami are problematic. I do not recommend both together; the males are territorial. In a 75g you could have a nice group of 5-6 angelfish; not one, as this is also a shoaling fish that will be better in as small group. But as male and female will be likely, expect spawning and that often means trouble for other fish. You can read more in our profile.
Mention is not made of water parameters, meaning GH (general hardness) and pH. Livebearers need medium hard or harder water and a basic (above 7.0) pH. Tetra, angelfish, gourami prefer soft, acidic water but some species manage in medium hard basic water if it is not extremely so.
Glofish are modified zebra danio, so that profile will give data. This is not a good fish to combine with sedate fish like angels or gourami, as the danio are active swimmers.
Lots to think about; hope this is of some help.