fully grown, they'll need 5 gallons each, and if 2 of those angel fish pare up, you'll need a 20 gallons tank and remove that 3rd one.
first, your tank is new, you should have only gotten one angel fish. but it's not too late to salvage your tank. do a 1 or 2 gallons water change every other day for about 2 week, then do a 1 or 2 gallons water change every 4 days for an additional 2 weeks, then as your bacteria colony grow, you may do a 2 or 3 gallons water change every 7 days.
as your tank is fully stocked now, don't add any more fish. not even a "sucker fish" they won't actually clean your tank, but only add more biological load. scrub the algae yourself, it would only take 30 seconds. if you ever have more room, avoid neon tetra, some species of angel fish hunt neon tetra for food.
my rule of thumb for any slim body fish is feed sparingly once a day, 6 days a week. the fast is to prevent the fish from over eating or you from over feeding. more fish die from overfeeding than starvation. never follow feeding direction on the bottle, they're direction is for you to use more food and buy more food. never feed 10 to 15 minutes. in fact, don't even feed as much as they will eat in 5 minutes. if you must use time, as soon as the flakes hit the water, set your timer on 45 seconds, remove all flakes after that. if you're feeding macro pellets, 3 pellets per day per angel fish will do.
don't put your tank by window, it's a death trap. if you want fast plant growth, you need real plant substrate and co2, but now that you have 3 fishes already, it is too late, the fertilizer substrate release ammonia, and once you add your plants, you're really not supposed to change water for a while. you can look into plants that require no substrate, fertilizer, dozing, co2, or bright light such as java moss.