I just use MiracleGro Quick Start to start the seeds. Then regular MG Potting Soil to grow.
Its only 60 days. Doesnt need much at all. I do put molasses in the water though. Only thing I add.
I grow the RRFs. And every plant so far has exceeded the companies stats. Company stats say like 11-16 inches tall. I got one now thats a little over 18 inches at 40 days. Think every plant Ive had with them, the smallest was still over 16.
That Rudulas (spelling?) in them makes them tough as nails. Probably could grow them in concrete dust lol. So you dont have to be to picky or stress over what to use.
Start simple, adjust and tinker as you go along.