My tip for filling the remaining hp is to fill it with blank panels until you get to know the modules you have. As soon as you reach for a function that isn't available, that's the next module you should buy.
-- farkas
+1 on that! Konstant Labs has a series of "telescoping" blanks that let you vary the area covered. That way, you won't need to buy a pile of smaller panels with fixed spacing. These come in 24 to 48, 12 to 24, and 6 to 12 hp sizes.