Depending on your area, the quality of well water can vary alot. I suggest you invest in a cheap TDS
meter, and find out just how many ionic disovled solids you have in your water. If your area has any natural copper deposits, you definately want to get an RO
unit. Copper is toxic to invertabrates, and stressful to fish.
Corals and other invertabrates can be very sensitive to water quality. If you were going truely fish only, I wouldn't worry about it, but with the urchin and the possiblity of an anenome, you want really high water quality. High water quality starts with pure RO
water, and is maintained with a protien skimmer. Many inverts (like the anenome) also need very intense lighting. If you're going to stick with fish only though, all you need is any old filter rated for your tank size, any old lighting, and a heater.
Are you sure you want to mix agressives like the lionfish and puffer in with the clown and damsels?