I set up a new HA install a couple months ago and didn’t write any YAML. It was kind of nice? The UI tools have come a long way and it discovered all my devices which had never happened before.
The thread you shared is worrying though, it’s the complete opposite of the spirit of FOSS. I should probably reconsider paying for their subscription at a minimum.
LiFePO4 batteries like being charged up high, so you’re probably fine keeping them plugged in.
You’re right about not going under 20% often, but you’ll want to charge to 100% at least periodically to allow the cells to balance.
Edit: Please make sure you’re looking up information on Lithium Iron Phosphate batteries specifically, they behave differently from standard lithium batteries and a lot of the advice shared here won’t apply.