I have 2 feet deep planters. How much of the soil should be cactus mix?
Here is a good 'recipe'.
5 parts perlite
4 parts bagged potting soil
1 part coarse sand
pinch of rock dust
If you purchase a cactus mix, mix this half and half with a good quality potting soil.
All succulents like a little bit of acidic addition. You can add 1 tablespoon of white vinegar to 5 gallons of water and use this to water your succulent planter.