Hi kpebbles, welcome! Glad you're finding this space worthwhile!
I'll let the folks who grow under lights answer those questions in more detail, but in general, the plants with higher light requirements should go beneath the centers of fluorescents, while things like Phals do better out at the edges. Your answer to question 2 is exactly how I would place everything if it were me.
If I remember correctly, light intensity falls off with the square of distance, so the lower leaves on very tall plants won't get anywhere near the amount of light the upper leaves will. Dends. can get very tall, so if you position your lights to accomodate one of those, your other plants on the same shelf may not get the amount they need. The Dend. might do better for you too in a location that's more evenly (and brightly) lit, to let the Cattleya take center stage on your growing shelf.