I have an area that is 24"w / 18"l / 56"h. Is this ample area for growing? If so, which plant would be ideal here, and how many of that plant could fit in such an area.
you could do a pretty nice 2 to 4 plant scrog to maximize you grow space....check out scrogs and maybe verticle grows.......t-5 veg....150 hps..........??? for flowey....endless choices
Fine for 2, possibly 3 plants. You have 3 sq ft but not a great shape for fitting 3 plants. Get yourself some 5 gallon buckets that are tall and narrow, that will give you a lot of root volume without a large footprint. Unused paint buckets from Home Depot will do, or if you have a cat the large plastic kitty litter bins work well also (in fact they probably would work better because they are rectangular and so can take better advantage of the small footprint).
See my sig. Plenty of room for two plants and like Toasty said, 4 gallon rectangular buckets work great.