Just make sure the nutes touch the roots a little. Probably not quite half way up the pots to start, then about an inch or so below the pot as the roots start growing out. The best thing you could do is get at least one air stone in there, and have the nute level about 3 inches below the bottom of the pots. That way bursting bubbles with spray liquid all over the roots, and they will get plenty of oxygen (the key).

I'm not familiar with those nutes so I don't know if they need tweaking.

All I know about lava rocks is that you need to wash them thouroghly before use, and also to not use them. You should consider clay pellets since they hold just the right amount of moisture. Less than rockwool, more than lava.