Hi app5774e,
Welcome to STS. Im fairly new to cactus and gardening in general myself, so others may have better suggestions.
First, id say definitely stay away from sand. Everything we read when first started suggested sand in the mix. Turned out to not be so great in our humid conditions and were a fair bit north of you. We switched to a pumice/perlite mix. Sand always clumped no matter what type we tried, and wait til you go to repot your plants and get a whiff of the roots. Gross.
For soil itself weve used just a mid priced organic potting soil and weve used more costly potting soils. Honestly, as long as your mix can drain freely im not so sure i can tell which soil was in which pots. But then again, the bags of organic mix that are basically mud and woodchips are about worthless. Spend the few dollars more if you can.
We mix ours 50%soil 50% pumice/perlite. Pumice can get rather expensive, maybe others can suggest a cheaper alternative.
Not too sure on the length of the growing season down there. Ours stop getting watered toward the end of september and are brought in end of October, unless the weather doesnt force us to.
Theyll go up in the attic where it stays cooler and dark until sometime in March. Other than the months where theyd be effected by frost, theyre outdoors.
Not sure what to tell ya for watering either. It rains often here and our plants take in all of it. Besides the rain, im also pretty liberal with the hose.
Do you have cuttings or are they rooted plants already?? Either way theyll need to be slowly acclimated to the sun, but a plant without roots shouldnt get water too often. We may water a cutting once a week or somethin like that, but opinion on that may vary too. Misting every so often will be ok.
Sorry to go on and on here. Hopefully others familiar with your region can weigh in and set it straight. Besides that, welcome again and wish you all the best with your new plants.
Peace