So I take that your Vivosun setup includes their self watering bases? That's cool. I think Nebula did a side by side comparison grow recently using that system. I use the autopot system. It's a self watering bottom feed system as well. You are correct about conflicting information. That's a good reason why I don't go anywhere else for grow advice but GWE, and if I have questions they get posted here.
I like this quote from that article about topping. "Wait Until Plant Has At Least 4-5+ Nodes – Topping a Too-Young Seedling Can Slow Down Growth. Waiting a Few More Days to Cut Can Result in a Much Faster Recovery." I top when the plant has grown 6 nodes and then make the cut at the 5th node. I let that 6th node grow until their is enough space from the 5th node to leave about a 1/4" stub after the cut. That helps the plant heal faster and stronger at the point of the cut.
Yes, if it were me I'd leave the smaller lower leaves alone for the time being. Let it grow out a little bit. You can defoliate it later.
Are your plants an autoflowering or a photo sensitive strain? Your grow environment looks sounds good. The PH is in the middle of the range for soil, that's good.
https://www.growweedeasy.com/ph. I like the graphic about soil and at what point in the PH range plants are able to take up particular nutrients. It's helpful. I use the one for hydro.
One question about PH is your water. Tap, RO, or distilled? Is is hard or soft? If it's soft you want a lower starting PH. PH issues are responsible for the large majority of cannabis plant problems. Always start there.
Do you check the EC of your watering solution? If not you might think about it. EC tells you how much stuff is in your water. If you live in the USA your local city, town or water district can give you an analysis of your tap water. It's a good number to know.
If you haven't already, invest in a quality PH pen and EC pen. Aspera gets good reviews. I use BlueLab equipment.
You've got good nutrients. Follow their recommendations but start at about 1/2 strength.