I would advise against -80 do to the wash. The low temperatures reduce the solvent activity too much and would take way too long. Better to start at -80 and go down to -50 or -30 or even -20. Try each out and see what works best.
What would be the efficiency of ethanol extraction at -20C.
At this temperature still chlorophyll being xtracted?
The Future4200 forum has several current comprehensive threads on extracting with ethanol at low temps, here's one for instance:
https://future4200.com/t/cold-ethanol-extraction/4068