Peppers take some time to germinate. I would say give them another week. If no sprouts then, you may want to buy plants instead. I'm not sure how long your growing season is, it might be better to proceed with plants. As for the rest, can you post some pics? That would help with your other problems. Most likely a good idea your wife had with the DE. Slugs will eat veggies close to the ground, and DE is a safe and effective way to control slugs, it that's what eating your garden.