I didn't know Target has it, cool! How much was it?

Yeah, this stuff is pretty much nutrition-less like straight up peat, only better draining, fluffier and higher pH.

You can mix in some compost/humus/manure or sprinkle Osmocote over it or keep up a regular liquid fertilizer schedule.

I don't see the point of mixing soil in with it.

Soil adds minerals. Many/most chemical fertilizers mainly contain NPK (nitrogen, phosphorus, potassium), and ignore all the other nutrients.

I know I'm late in adding this, but you might want to look at the comparison by Utah State :

Here is a link that might be useful: Utah State coir/peat plant growth