Do I really need to have 20cms from the top to the light?
How much do you think I will yield? I know that there's no way you can guess but you can try eheh.
And can I use a pot that instead of being taller it can be wider, will that work? That would reduce the height of the pot.
Yes a CFL can burn your plants! The base gets very hot, so does the portion of the bulb closest to the base. You can use a wide pot, roots will grow to the sides when they can't go down any farther.