Birdsnest can be weird, they sometimes just die and if you don't have a lot of SPS to indicate if it is just random you may take actions that wouldn't be necessary. Montipora caps are the easiest and don't require the quality of water that other SPS do. A two part solution is going to be the easiest for you, if you get into SPS later and have a high calcium demand then you can look into a calcium reactor. Flow is incredibly important, not just a high flow rate, but flow that is high and then lower, like a wave passing over them. This intermittent flow is what most SPS keepers use and it seems to work for my tank. SPS aren't super difficult to keep, but your tank needs to be stable, if the levels of calcium/alkalinity, nitrate, phosphate and nutrients fluctuate, the SPS are going to respond negatively. I would look for frags that have been captive grown and are suited for tank life. Colonies are not only expensive, but they often adapt very poorly to tank conditions as many are taken from the ocean. You should be able to find some good options at liveaquaria.com. They have a frag section for SPS that are good and hardy; you might not find some of the mind blowing colors that you see at other places (atlantisaquarium.net comes to mind), but they aren't super expensive and are nice. Also, what lights are you running? Good lights are vital for success in SPS, cheaper lights often have a poor PAR reading and can affect the color and growth of SPS that might not be as easily noticed in LPS.