Welcome to the community! Your girls look pretty happy.
What pH do you water at?
If you can share a pic of the meter you’ve got, chances are someone here has it or has used one and can help you out.
There is definitely a lot to learn. Since you’re in flower already, I would just keep reading around on the forums for techniques other growers use. “FIM” and “top” are nearly interchangeable ways of saying “removing part of the plant to make her grow more offshoots/colas” - key difference being a FIM can produce 2-4 offshoots where a top will generally net 2 offshoots.
The SOG/SCOG/SCROG thing still confuses me but if I’m honest it all seems to translate into using plant trellis or netting to keep your canopy even.
As far as for new growing and critical musts, understanding the DLI production of your lights is a must. Check here:
Next, understanding the PH and PPMs you need/want during every stage of growth is very helpful.
Here are a couple charts you’ve probably seen around but I keep handy for my own reference.
