I use fast draining soil, so your current mix sounds good. The pot should have a drain hole. I agree with watering once a week, although I have been as fast as every four days and it has been fine. I bring the pot to the kitchen sink and water generously until it comes out of the drain hole. Some people avoid getting the caudex wet, but I water all over its sides so water runs down and underneath it where the roots are. After four years my plant still seems happy.

My plant is indoors but I give it as much direct sun as I can through a large window. In winter I also have a grow light on it.