I've used FF Happy Frog for years with no problems at all. I didn't like the mix or the price of the OF half as much.
I always mix in some of this to keep the soil from compacting and to aid in drainage:
And a little dolemite lime will help to keep the Ph of your soil in check over the long-term.
I do have to say though that I really think you need at least a 6" in-line fan and ducting to even begin to try to keep your temps down in that tent. I really don't think that 4" setup is going to swing it for you, unless you're in a cold-climate area. If you've never grown with high intensity lights (400w+) you'll be surprised how much heat they put off and how fast the temps rise. Heat will kill you if its not addressed immediately.