It’s hard to tell if they are eating enough or too much without keeping track of their weight - definitely recommend the scale as suggested above. With a scale you’ll find that you figure out what they’re normal weight patterns are and you’ll work out routines that support that. It’s great that you are thinking about it early!
Just as examples - my conures usually have pellets in their cage always, I find that they eat a tablespoon or two of pellets each per day. Mine each get a small spoonful of chop morning and dinner (and I take away leftovers after a few hours). Mine have things like Zupreem pure fun or seed mixes on their play stands so that they can get a few seeds and dried fruit while they are out and about. I tend to give things like nutriberries, oven baked bites, and other “loved” items as treats - not every day, but regularly. I find that mine, like Laura’s, like to forage and work a bit for their food. I have a selection of food puzzles that I rotate in and out of their cages. Mine seem to enjoy moving around and getting food/water from different locations in their cages.