How early to top and how many times for potential mother plants ?

how many clones you intend to take at a time? that will dictate the size of mother plant you want to maintain. when i kept a mother plant i was tight for space, so i didn't want to cut it unless i had to, because eachtime it's starting to grow from a higher point and vertical space is lost each iteration. If you need to mainatain size you'll regularly cut it back and let it grow back out. Train it out horizontally and top or continue to lst until you have as many vertical branches as necessary to take "enough" cuttings... each one might be able to provide several cutttings depending on how large you keep your mother plant. plan to take more cuttings than you need to cover any potential failures. I only wanted 4-5 cuttings at a time from any 1 mother, so i kept my mother plants small. Still had to be smart about pruning the plant over time. I always made sure i had enough growth leading up to taking cuttings. if in same pot for long enough, you'll also need to do some root pruning or simply regenerate a new mother plant. It is utter nonsense that this in anyway reduces quality of the plant. clones are all the same age and identical, genetically. Don't take a limb that's all fucked up and you'll be fine, lol.

I guess the prequisite for mother plant is to have as many internodes as possible, topping helps with that for sure. The phonemenon called "apical dominance" is when main stem is given a lions share of "total energy". This is the natural way for a cannabis plant to grow. If you bend down and hold down the apex of a cannabis plant so that the main stem is same height as lower stems. After a couple days the plant will reasses its life choices, it will then redistribute the energy to stems with higher or equal light intensity. Ideally top once then bend, the Initial topping will send a wave of hormones through the plant forcing it to send energy to other stems. Every stem that receives relatively the same light Intensity will now grow in unison towards light. Apical dominance is broken. If I was doing a mother I'd not top her once. But that's just me. Best of luck in the new year.