Welcome.
20 gallons long has a nice foot print. But because of that, you may also need equipment for a large tank with that same length.
I would consider at least an AI Nero 3 wave maker or a gyre pump to be able to reliably push water over the length of the tank.
For light, you might consider two AI Prime 16HD or similar for coverage. A cheaper option would be to run a 2-4 bulb T5 fixture. You can by the more expensive reef specific fixtures or those designed for indoor terrestrial plant farms.