First--28" high and you're still in veg? Wow...that's going to be a serious plant. With a plant that size you will definitely, 100% need more light, especially below the canopy. Even though the bulbs you list (which are interesting, btw) are considered spotlights, I just don't see you getting heavy canopy penetration from a 20w bulb. I also wonder if you're going to outgrow that area. You're going to get some stretch and bushing out. A 28" plant should grow at least 1.5 times in height in flower...it will probably double in height or more, depending on the strain. A 4' plus plant is probably going to need more than a 24" x 24" area. And I stick with the basic lumen information...if you end up using 28" x 28" (which I think you'll need for a plant that size), that's around five and half square feet. That would mean at least 10 bulbs like that; 15-16 would be a whole lot better. For cuttings, if you plan on staying in the 24" x 24" area...that's four square feet. At least 7 or 8 lights; 10-12 would be best. I'd think about having 65-75% of the lights on top, and 25-35% below the canopy as supplemental light. I've used CMH bulbs. 3000k is pretty normal for those types of lights. IMO, they're as good as MH for veg, but not quite as good as HPS for flowering (close, though..more than good enough). They run cool, which is nice--and you'll want to get the lights close, since they're only 20w each. You'll need plenty of lights though, as I said, so be sure and check temps and have some air circulation. Good luck!