Soil help please

I need help on soil to use.

I heard ocean forest is good but too strong for seedling...so this is my setup.

I'm going to buy these cocotek plant liners: CocoTek Liners - 2", 20 pk - GROWING MEDIA - HYDROPONICS - GM-CCGH-2

Because the roots can just grow right through and I can put that pot in a smartpot in like a week...the last time I tried to transplant it crumbled in my hands...so I'm not doing that anymore.

What soil should I put in those pot liners and also will it be bad to just put that pot directly into another one because it would be 2 different soils?

Also, if you have another suggestion for soil I might check into it..I've been hearing FFOF has gnats and pests in it..

Ocean Forest is not too strong for seedlings. No soil is. I use both MG soil and OF soil with seedlings and I start fertilizing at 1 week of age. Never burned a plant yet.

and no, FFOF does not have gnats or pests. Those come into the grow room other ways.

The soil won't "crumble" when transplanting if you wait until the roots are well developed, they hold the soil together very well.