Once they turn grey you can store them in the frig for several months. Just be aware that if you keep them on the door or and area that warms up they will start hatching in the there. I once made the mistake of keeping them in the crisper drawer of our garage frig, well when we fill it with warm beverages the frig warms up at first and I lost thousands of them.
They are easy to hatch. I keep the eggs at room temperature and they take about a week to hatch. Raising them can be a bit time consuming, but it's not difficult either. If you raise them it ends up being a fraction of the cost of buying them in the store.