I wouldn't start them in the 5 gal. buckets. Start-out with cups or small pots, and transplant when necessary. Let soil dry a bit before transplanting...this keeps the rootball intact.

In emergencies I use MG, too. I've also been forced to start seedlings and cuttings in it. It actually works better for my clones and seedlings, than the super-rich medium I usually use. (I refuse to pay $6.00 for a ziplock-baggie-sized bag of seed starter mix) Anyone that says the MG doesn't work has a hole in their head. You just have to remember what you are working with, and adjust to suit needs, and don't overwater.

Curious: Why not just use a 1" to 2" layer of rocks in the bottom of the buckets for drainage? Any type of soil in the bottom will restrict airflow thru the roots system, and prevent proper drainage.

Since MG has some nutes already, I don't add nutes for about 3 weeks to a month, (unless seedlings and clones start showing defeciencies) then start with 1/2 strength Fox Farms veg. and micro-nutes, and watch for how the plants react. Best to sneak-up on the maximum dilution strength your plants can handle, then to start-out too strong in the first place.

During the summer, the moisture control mix is ok, but during the winter, or when starting seeds or clones, I add approx. 20% more perlite, for better drainage.