Since I've never used coco before I'm not really qualified to help with the ratio... I use around 40% perlite to lighten up a heavy, sticky, COMPOST media...now, coco; well that's naturally much fluffier to begin with so it stands to reason you could use a lot less perlite.
I think you might have seen promix being listed as pH neutral... I think they must treat it or something... it's a peat-heavy media.
If you aren't totally in love with soilless I still suggest using as much composted humus as you can get your paws on because the pH is so stable and the organic acids are great for your plants.
If you go with coco, or any other soilless, you might try watering with topmax even in veg, or Soil Syrup (very cheap source of humic acids that you would otherwise get from composted leaf clippings etc)
I've just begun using humates in veg and think they're great.