I think you're on the right course.Purpling stems in my experience have nothing to do with over or under feeding ferts,it's a genetic gig
Looks like 15 plants altogether,how many are known females are how many are seedplants?Are those 1 or 2 gallon containers?I sex my seedplants in two gallon containers I'm not potting up unless I know they are females.How much height do you have to work with?Are you planning on flowering in those containers?Obviously if they are mostly females you pretty much have to by the looks of your space.I notice you started in those conatiners,next time it may serve you better to start in smaller ones and pot up as the roots fill the container for space sake.I even start my clones in smaller containers{4 inch nursery size or some folks use 16 oz beercups} and pot up. I start in my seedling container,pot up to veg container 2 gal. where I determine sex if seedplants,then pot females up to flowering comtainer 5 gal but a lot of folks use 3 gal.The difference in yield between 3 and 5 gallon is pretty significant actually.Its just better for a number of reasons to use multiple containers than starting out in a larger container.To me 1 gal is a larger container and wont grow out seedlings in something that large,a lot of folks do its a matter of preference.Looks like you got a good grip on things