We need to air seal and insulate! How would you decide whether to do that at the ceiling or at the roof in this instance?

Climate 3A W/H. Typical 2000’s north Texas roof construction — single story, very tall roof over the attic. 2400 sqft, two whirleybirds, lots of soffit vents, and many uninsulated can lights that are venting into the attic…. and drop scorpions on us.

Just installed a hyperheat ducted air handler, and yes, it and the ducts are in the attic. (There was no good way to bring all that inside the currently conditioned envelope with available local contractors.) New ERV (freezeproof with no drain required) and ducts are up there too.

I would love to insulate the roof, seal the soffits, and move to a conditioned attic, but I’m scared of putting spray foam inside the conditioned envelope due to VOCs. GWP is also a major concern although I have been researching HFO-based closed cell foams. Is there some other solution than spray foam for this that is commonly installed in my area?

So I instead considered air-sealing the ceiling and then applying new cellulose to R-60. Any foam that would need to be used would hopefully vent to the attic. Two problems: 1) almost all home electricity cables are stapled directly to the ceiling joists and 2) we have PEX everywhere in the attic… which just froze last night lol. So I’d hate to put spray foam on the ceiling and then make future electrical maintenance difficult and still have freezing pipes.

I would love to hear thoughts on the best path forward here, and any recommendations for north Texas insulation contractors with an environment-forward focus.

P.S. thanks everyone for the previous help here: https://www.greenbuildingadvisor.com/question/variable-speed-air-handler-paired-with-minisplit-style-inverter-condenser