Hm.. I had some trouble with a hovabator overheating my eggs last year after a power outage. I just go with Flexwatt hooked to a Helix thermostat.. works like a charm.
As for substrate, I mix perlite with larger-granule vermiculite (not the powdery stuff.) I got both at Lowe's last year and still have plenty left for this year (unmixed.) It takes some experimentation to see how much water to add in my experience. I make it just moist enough so that you can wring a little water out if you squeezed it tight, but not much. Towards the end of incubation, I had to spray a little warm water in (never onto the eggs! In a corner..)