donkeman
I raise 10s of thousands of Cattleya and think they are about the easiest after Dendrobium.
Indoors you have a problem with flowering, because even in a window sill you may not get enough light. However, in W Va you can take them outside all summer and that will be their best blooming season anyway. This is what I would recommend.
Temperature range is quite extensive for cats. I have mine outside and the temps go to under 35 and over 100. Humidity is non-existent in the winter and 4 hour a day of rain in the summer. I just ignore it all.
With young Cattleya the light levels are not important. Until they are blooming size lower light is an advantage.
Water would be best out of your RO. The well water would be OK if you need larger quantities. I would avoid softened water because softeners sometimes allow some salt to come through. The RO would remove it.
I use two fertilizers. Worm Tea is my favorite (concentrated liquid worm manure) and in the past I have used a balanced 20-20-20 fertilizer at the rate of 1/2 to 1 teaspoon per gallon of water. The brand is not important, although, many people do not like Urea based fertilizers. I have never noticed enough of a difference to matter.
Really soak the Cattleya. If you only have a few I would suggest a dunking every week for 30-45 minutes. It takes a while for Cattleya to absorb the water necessary to grow those big plump pseudo bulbs. Let them dry before the next watering.
Look for miniature or semi-miniature Cattleya for indoors. They also have a tendency to flower easier and in lower light levels. Keep them pot bound.
Here are two of my favorites.
Loveknot is a semi miniature (3-4 inches tall) with 3 1/2 inch flowers
Sogo Doll is a semi miniature (8-10 inch's) with clusters of 2 1/2 inch flowers
There are a lot more that fit the bill for window sill growing.