I'll answer your your questions in order.
A. The strips are approximately 8" apart center to center. You are limited in how far you can spread them by the length of the connector that daisy chains them together.
B. I have grown and successfully bloomed all types of Catts, Dens and Oncs with just the two strips and the light from the window. The Phals, Paphs and Phrags are all doing great and bloom like clockwork.
C. My experience with these particular strips is that the heat dissipates quickly because it is not trapped under a hood. I also keep all of my plants on humidity trays, so the rising heat hits the bottom of the tray first warming the water not the plant above it. I have had plants practically touching these lights with no problems. That said most everything I'm growing is intermediate, warm to hot growing. Anything that requires cooler temps is on the bottom shelf and father away from the lights.
D. At the height of my orchid insanity I had 95 plants on that one rack. I'm now down to 45 intentionally.
E. The lights are all on a timer. They get 11 hours of light in the fall/winter, and 14 hours during spring/summer. The lights are all plugged into a power strip which in turn is plugged into the timer. The window the set up sits in faces southwest so it does get a lot of light. I would imagine if I were growing in a dark basement I would have to add 1 more strip per shelf to bloom things successfully.
I also keep a spreadsheet of when I change the bulbs and what location on the rack. I know I don't change them out nearly as often as I should, but it doesn't seem to be hurting anything.
I had just been contemplating whether or not I should add 1 or 2 T5 strips to my racks in my south-eastern window... And I bought a cheap light to see..... But I'd started to second-guess myself... And then I read ur posts & u answered my doubts! 
(*obviously everybody's grow spaces, conditions & culture are different, so I do understand that it is still mostly trial and error, no matter how similar something is* but I was second-guessing myself! Not to mention, I should have a few more blooms at this time of year! 
Lol ~new set-up~ 
{I've doubled my collection in the past year 
})
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