What's your table size? 4x4 should be 40 gal, 2x4 should be 25.
You can flood n drain RW. You MUST pre-set the pH of the slab FIRST before adding plants!!! The flood cycles will be less frequent than a more porous medium like hydroton. Personally, I prefer HT for flood n drain and coco for drip, but if you already bought your RW slab, then get your table set up ASAP so you can get the pH adjusted while the seedlings are rooting.