You would probably be better, long-term, using LECA instead of a perlite/charcoal blend. In addition to being friable and apt to crumble under root-growth action, the perlite carries a lot of potassium with it, which can lead to fungal resistance issues in the future, and while the charcoal absorbs really well, it doesn't release solutions well, leading to more-rapid buildup of minerals, and the need to replace it.

You really should get almost all of the sphagnum off of the roots; it will decompose eventually, and is a risk for maintaining a pathogen-rich environment. I would not suggest using a preventive fungicide treatment, as evaporation of the water will concentrate it, potentially to dangerous levels. Same is true of fertilizers.

I recirculate from a sump, and replace all of the solution weekly. If you can rig up a standpipe and a timer to periodically overflow it to the drain, it'll reduce the labor significantly.