What kind of cal/mag woes are you referring to? I'm growing dwc if that helps. I'll check out the light!
With leds you need a fair bit of control of the environment, its cold light and wont have the same drive to transpiration which means the plants may not uptake all the calcium it needs. There are easy solutions though: little bit more heat and or adding a bit more calmag.
Although i do like the cmh: grows fairly similar to leds (accepts higher temps without so much problems as hps for example and seems to always outdo their paperspec) your space is a little bit on the smaller side, you will probably have some heat problems in there.
And yes, you can ignore OHD, while he is right that leds can manifest calmag issues which can be a pain to chase down if your not used to it, as you can see he is more interested in arguing with people from his troll history than actually answering your questions and helping. Also a lettuce grower mainly afaik.