The easiest way to know about how much to feed is that if you are feeding too much you will see the uneaten food on the bottom of the tank. If you are seeing this you know you are feeding too much.
Siphon out the uneaten food and reduce the amount you are feeding a bit. If there is still uneaten food, repeat the above.
There are many sites which say only feed what the fish can eat in a few minutes, the problem with this advice is some species are grazers and tend to munch on and off all day. A good example are discus, but there are other species as well. This is information we should have before we get a species than after the fact.
Small fish do not eat a lot
It is best to feed the sort of food which will be in the areas where the fish are active. For corys and other bottom dwellers sinking food works best.
Finally, in my experience all fish are pigs. They will try to eat anything they think might be food. The only times I have had a fish refuse to eat is when they were sick.
If you want to feed sinking foods for the corys be aware that the tetras might try to grab them in the way downif they can. I tend to feed all my tanks in the evening before lights out. But I used to feed 20 tanks with an assortment of fish and I have a fairly good variety of foods especially for different species. I have corys, plecos and loaches as well as mid and top water fish. I have a few shrimp as well.
When I feed thw 150 thei the clown loaches and redline barbs, it feed my flake mix for barbs and singing food for the clowns, I put in the flake first and the big clowns will eat it as soon as they can, This helps when I feed the sinking foods ads the biggest clown at almost a foot will eat sinking wafer, stick and pellet food before it hits the bottom and gets a bit softer. he is my super pig.
My best geuss is I have over 20 different foods. But, that is because I make my own blend of flakes which uses about 6 or 7 varieties. I have this many because of the various fish species I keep. About the only food I do not use is live which is usually the best option if one can do this. It is most helpful if you are spawning fish.
edited to fix typos