24 ft square is about as big as you want to go with a single 1k light, so if you can fit them all in that space you will probably be fine. A 1k light is about 130,000 lumens roughly, so 130,000/ 24 = 5416 lumens per square foot as a rough guide. keep it inside 5x5 or you will need that extra light.
The issue really is, how tall do you want your plants to be. With a 1k light you have effectively 3 foot and some change vertical (because of lumen drop off beyond that distance) then nothing but popcorn and then die off below that distance from the light with the canopy in the way. Then the...
If you don't feel the need to completely micromanage and know the exact numbers the CAP PPM-4 seems to be a good option. It can be found if you really look around for about $200. I recently started using one and it seems to work fine. On at 1450 PPM off at 1500 PPM.