No Title
You can use that plant food if you are very, very careful.
1. Don't over water. Cannabis roots Love air, but need some water.
2. Don't use that stuff until 3rd or 4th node. At least. By then you'll need to be in more soil, bigger pots, something with good drainage. If you add some healthy natural soil to the mix you will gain some micro nutrients and pH buffering. Straight potting soil is great for drainage, but not well rounded.
3. Whatever the directions on the box say, use it quarter strength. Watch your leaves. If they are dark green, just use clear water. I don't know the fertility of your potting mix, so you'll have to let your plants tell you.
I love your Diy attitude.
For really great breathable pots, get some landscaping fabric and sew some up. I'm including pic of what I use.