The Asta lights are really interesting... I've never used a spot light like that for aquatics. On a long tank like this I'd almost definitely go for 3. Are there any significant up or down sides to them?
A brighter life, raised higher, will give you more even lighting levels throughout the depth of the tank. If you have to put your light very close to the water to get proper par to the substrate, you'll have extremely high par at the upper levels of the tank. A stronger light raised higher can help mitigate this.
I think you'd want 3. I've got one on an 11x11 tank and it doesn't seem like there's a whole lot of spill over. 1 upside is that I don't think there is a non-pendant/single source point light that fits your tank. Your either going to be short or hanging over the ends. Another upside is with separate lights you can direct more or less light to certain areas. I have some buce and anubius up high in my tank on top of some rocks. I keep those lights turned down a bit when compared to the ones that are lighting plants that are deeper. It's kind of nice that they come with their own gooseneck mounts. It also comes with a supplemental lens but I remember the light being a little uneven when I tried it. You said you wanted simple on and off. It's got a built in dimmer. Just adjust and put them on a timer. It's a fairly bright light. I get enough light in the bottom of my low tech 5 gal Marineland Portrait tank and it's 17" deep and I think I only have it turned up 1/2-3/4 power.
I had one on my fluval spec v for a couple of years. I think for the price its the nicest light available for the area they light. They don't have a fan in them either unlike a lot of other pendant lights so they are silent.
