It's pretty darn hard to overfeed a bird (maybe with the exception of some amazons which have a tendency for being "perch potatoes"). Especially with a young, energetic bird like a conure, I really wouldn't worry about feeding too much and would instead be careful to avoid the opposite!
One rather fail-safe method of determining just how much your bird should be fed each day is using a gram scale to measure their average daily consumption. Simply weigh your bird's food in the morning before breakfast then weigh what's left right before bed. Subtract the second reading from the first to figure out how much your bird ate that day. Then do this for at least a week and average the values to determine the approximate amount of food your bird eats each day. This value can then be used to portion out your bird's food if you are looking to reduce waste or ensure they are eating a varied diet. For example, I know my parrotlet can eat ~4g of pellets/seed mix each day. But because I want to also make sure he is eating a variety I only give him 2g of pellets and a heap of veggies/fruits/chop/mash. That way he can't gorge himself on his favorite food alone and is hungry enough to eat a bit of everything else.
This method works well enough if you have a picky bird like mine but can be inaccurate if your bird tends to waste a lot of food (by throwing it out of it's dish), or if you are trying to weigh wet/fresh foods (which will vary). Also, if your bird is still growing, their appetite may fluctuate. Overall, I tend to use the values I've surmised as mere guidelines, and mainly because I hate throwing out a lot of uneaten food.
On the other hand, if your bird is really good about eating everything there is no harm at all in feeding more than he needs. A lot of people will feed their birds a bunch of cooked mash or fresh chop in the morning, for example, then let their birds graze and eat as much as they want before removing the food in the afternoon.
Regarding your question of just how much to feed of eat type of food, there really is no set answer. Overall variety is going to be your best solution, so don't be afraid to feed more of one type of food one day and another the next. My birds go through a rotation of cooked mashes every week. Day 1 might be pasta-based. Day 2 might be a bean-mix. Day 3 will them be a mixture of whole/ancient grains. Each day will have an addition of fruits, veggies, and fresh sprouts.
In general, your conure's base diet should be made up of a pellet (40-50%) and seed (10%) component. I like to feed mainly sprouted seed which is more nutritious than dry. The rest can be made up of mostly veggies (dark leafy greens or orange/red/purple veggies are best) and some fruit. The legumes/grains can be cooked and added to the veggie mix if you'd like.