hi
keeping your cacti at around 15C will help them remain dormant, however while dormant they would love direct sun to continue their other functions like fruiting and rooting etc
i guess your soil could use some large sand and basalt rock, otherwise you could mix that with 30% living soil from some producer where you are, or if you can't buy it creating living soil is a laid out job taking something like a 6 to 12 months, which you can mix with your main soil so the cacti actually thrive, and that has a sign, where your cacti grow in an almost tube like shape, no ribs
for artificial lighting using vegetative LED chips would be the best way for cacti, 5watt blue (420nm) LED chips and 5watt UV LED chips, so thats 300watts (60 chips) blue and 30watts (6 chips) blue for 65x65 cm, use quality spherical reflectors for the chips and not lenses
you can read up blackdogled website info about making leds so you can make proper leds for your cacti, the difference is that you only need those 2 chips
feed your cacti a aminoacid source, for example bioradicant from spain or something from general hydroponics,