There have been a number of threads over the years that explained super cropping rather well, some or many with pictures, so you might want to try some grouping of words in the search engine and see if you have a few really long threads to read through that will answer all your questions. It can be a pain but gold can be found if you try.
Another option, though I would not be able to recommend any particular one as being the best, there are a number of videos on YouTube about super cropping. Some are short and cheesy and others are long enough to be in several segments and both show and tell enough to get someone new going and then after that they can learn the finer points and tune things up a bit for themselves.
Just to be a tad bit technical, you said; “Is it best to top a plant young and then super crop so there is no main stem?” It is not that there no longer is a “main stem.” Actually instead there are two, three or four of them depending on how and when/where you top. The removing of a plant’s main leader will only mean another main leader will take its place. Depending on when and where and how topped multiple main leaders will begin to grow, four of them are common.
Their growth began after the rest of the plant and they do not get as much veg time and then they get the slowdown in growth after being in flower a while so indoors for various reasons they don’t always get as impressive looking to the eye as one very large singular cola and the single main leader that goes with it can, but regardless of yield being better or worse or how a plant looks, when you cut a plant’s main leader you do not actually remove it. Instead you multiply it and the result is you end up with more of something, that just looks ‘different,’ rather than less or none of it, but for some inexplicable reason some people still call it none.
Possibly it is in code and it really means “Climb Mount Nitaka,” likely not though, but whatever it is it durn shur’ don’t maka’ a heap-a sance ta me, ma’sef. But maybe that’s just me.
