Advice a rookie please

Trimming the bottom third of your plant is also called "lollipopping" as it looks like a big cannabis lollipop at the end of trimming lol I would also do your trimming that you are going to do very slowly so it does not shock or stress the plant. Towards the end of veg, I would take about 5-10 leaves at a time, every couple of days. Let them recover for a few days after removing some of the leaves, then do it again. Let them recover, then do it again, until your satisfied. I usually do it about once a week at the end of veg, and once a week during flower. Only remove yellowing bottom leaves when they are completely yellow and crisping up. If they are yellowing it means the plant is using them for food, so leave them until they are finished with them, or let the plant do it. When the plant is done with the leave it will actually discard of it. If you pluck it while it is still green then the cannabis plant will just move on to another leaf.