idk about adding the vermiculite to the coco, have not ever seen it done,
i think it would be just fine tho, its been in every peat mix i have used,
that being said, i also think… your 70/20/10 ratio looks great.!!
if that is what i had it would be put to use in that ratio.!
i m currently using 70% coco with 30% perlite, works great.!