Welcome to ATP!!!
Plant that milkweed, it will attract different types of butterflies while it is in flower but only Monarchs will lay there eggs on it. They will not bother your vegetable plants.
I have not tried crushed eggshells. Yes, they are a good source of calcium but much too slow to break down to be of any help on a container.
There are many good organic fertilizers. One of my favorites is Neptunes Fish/Seaweed liquid fertilizer. I use this on my flowers and veggies both.
