Hola Mari! Mira, just buy the best quality potting soil mix you can find. You can literally feed the plant *all* it needs with urine, it just needs to be diluted. Don't mess around with coco coir, don't mess around with anything that *isn't* soil right now.
Make certain the lights are measured in Kelvin and are 4,500K-6,500K.
Ahora, there's a difference between air circulation and air ventilation. If it's getting too hot inside the closet, you need to ventilate the air. I think the easiest way to do this is to have something pulling air out of the space near the top (heat rises), and then to have an opening that acts as a passive air intake at the bottom for fresh air. If you can ventilate the warm air directly outside, even better.
Y, keep in mind that the plant can appear to be heat burned, but it's been physically burned by improper pH, or salts in the soil (anything concentrated and especially blue).