Eggs should only be given occasionally. They need calcium 5x a week and the one time a week that eggs could be given isn't enough. Dusting your feeders or the veggies are the best ways other than phoenix worms, which are already high in calcium.
Yes and yes. You can tell when they have too much when their urate has a yellow tinge to it. I don't know how long this has to go on for it to become bad, but once you see it, back off a bit. A good way to remember how much, for younger beardies, one feeding a day, 5 days a week dust all the feeders. If they get to the 35-40 mark, you can probably stop there for that day. That's more of a guess than anything. But don't worry too much about overdoing it until you see the yellow urate. And also give lots of baths.