Thanks for answering my questions, and I appreciate the detail as well. Your plan is not far off from what the best growers use. I veg with a 600w blurple on veg only, which gives mostly that 6500 spectrum and some UV as well at 36" and then above that on both sides at around 45" are two 3500k cobs to help add some red spectrum and yellow, but less intense. Then, kind of like your system, I am watching the plants and trying to get lights closer. I have two 150w leds in opposite corners which get turned on in first week of flower giving me a total of about 570w led for my 4x4 tent.
Messing with spectrum and intensity together can really optimize terpene, resins, and yield. Yes, for your situation, adding another 3500k for flower will help give you a better balance and the plants will stretch a bit more with the additional red and far red from that 3500.