Good drainage is usually a soil with a 1/3 mixture of sand.
My recommendation would be 1/3 vermiculite, 1/3 sand and 1/3 peat moss (if you live in north america, that's easy). Vermiculite absorbs water, sand really doesn't (and is therefore good drainage) and peat moss provides some air for the roots while retaining water.
The best soil is also a sterile soil. You can cook the soil for 3-4 hours in the oven at 200C to kill off germs and bacterias if you compose your soil in the backyard. Although for seedlings you're really better off with sterile materials in the bag.
Green thumb trick; to setup a good pot, wet your soil in a separate container with some water to make it absorbent by playing with it. Good wetness is snowball capable dirt. But definitely not muddy. If you use peat moss and don't do that, it will never take the water.
Or just grab a bag of cactus soil at the supermarket, they're not that rare.
For Lophophoras, *apparently* a small addition of dolomite lime will benefit them.
Limestone seems to work as well as dolomite lime, I've seen some nice specimens living in crushed limestone from a river bed. Just make sure not to pick up any soil material from a salty beach area, the salt will eventually block all the nutrients in the soil. (Ah, not sure what the soil is in the pictures above, but that looks like a vermiculite/agrolite-covered soil).
Finally, lophophoras enjoy a basic soil around 7.5-8.5, depending on your water quality you might have some adjustments to make to get good nutrient absorption.
If you got a pH meter, that's easy to test and adjust. This is optional somehow. But it can definitely shed some light on bad growth if your tap water is acid though. I would check that first if you're starting with plants.
Based on that, you can also opt for San Pedros, they prefer acid environments. I personally find them more rewarding as growth material, faster, bigger, and in the end, just more and it's legal.
If growing from seeds, you can easily fit 50 to 100 seeds in a 4x4 container. With the germination rate factor and their growth, it should not get crowded before 2-3 years. Germinating seeds in too much soil can also make them feel pretty lonely ... they'll depress. These guys are social, pack them up !
I would also add that you shouldn't bother with 10-20 seeds. Increase your success ratio and pot 100 seeds in 2 or 3 pots (100 per pot). In the long run, you'll increase their survival rate.
The best containers are also those terra-cota, unglazed pots. 4-6 inches deep for seedlings, and perhaps 10 for big adults. Well... depending on the variety I guess. Fill the pots to 1-2 inches from the top and spread the seeds on *top* of the soil. You can then cover with one layer of white rocks (agrolite or crushed rocks), the whiteness provides good temperature control for the soil, some means against fungus and support for the seedlings. Furthermore, the whiteness allows the light to reach the top soil, which those babies require for germinating.
Williamsi is the one. The others are rather oddities.
Hope that helps. t'was My first post !