The simplest thing would be to buy a pre-mixed organic potting soil (for reefer). During veg, you'll probably transplant every week or two, and you won't need nutrients at all during veg. Do the final transplant about a week before flip and you're good for another 3-4 weeks before you have to add anything.
BUT have epsom salts and cal/mag available and decent flowering nutrients before the plants use up the nutes stored in the soil.
The best pre-mixed organic soil I've tried recently is Lush by
Roots Organics. Mixes like 707 (also by Roots) and Fox Farms Ocean Forest only have a couple of weeks worth of nutrients, which is fine, but not if you want the easiest way.