I would say if they are 3-4 inches thick you could possibly have a psychedelic experience with one cutting. Bridgessii is 2-3% by weight, and you need 500 mg to have a worthwhile experience.
Been a while since I read up on it but I am pretty sure that is an approximation of the mescaline by weight ratio coming in just under Peyote for the heaviest mescaline content.
Go buy some cactus soil and simply put the cut end in the dirt and leave it alone until it shows fresh green growth at the top and is anchored into the soil. I use Miracle gro Cactus/citrus soil blend and my cacti LOVE it and thrive in it. You don't water it whatsoever until it shows growth and has roots, or it can and usually will get rot and die. It has to be rooted and taking up water before you start watering it. They can take a long damn time to take off in my experience, and this late in the summer it will probably not start growing until next spring unless yours root faster than most of mine. You want to keep it where it gets a little light but not full sunlight until it takes off.
They grow pretty fast, but the Bridgessii don't put on near as much growth as Pachanoi and Peruvian torch do. Mine put on 4-6 inches every year. I can't stress enough that you don't want to water them until they take off and to go look at some pictures to see what a properly scarred over cut looks like so you know if it has been long enough since it was cut. Most of them I have gotten were well scarred over, but some have come pretty freshly cut. Might want to wait a couple weeks before planting just to be sure if you are not confident they have been cut long enough.
You will come to find that they come with big spirits, and that they are damn near cognizant beings in my opinion and I find it very hard to take cuttings to ingest from my own lol
Good luck and welcome to the joys of growing Cactus! I LOVE mine!
One thing to watch out for is cactus soil mix in stores. It holds way too much moisture and you are bound to have heaps of problems. Every brands cactus mix is this way. You want a minimum of 50% mineral pumice rock, course sand, coarse perlite, lava rock and then 50% or less of organic material. Being that bag of cactus mix or top soil or potting mix.