Fiat,
No need to feel like you're ignorant. Everyone started somewhere and even the "experts" don't know everything there is to know. I've been growing plants for years (not as long as some folks on here), but I learn something new all the time!
I think Miracle Gro by itself won't be fast draining enough, amending it with perlite would be better IMO. Okay, I didn't realize the pot was a couple inches larger than its previous pot. It still looks bigger than I would put one of those in. Maybe a 4.5-5 inch pot? Depending on where you put it, they may not bust out the pot as fast as you'd think. The lower the light, the less water you'll want to give them, the less they'll grow. Sans can take direct sun (I have mine in a sunny window), and while they say "low light," they really want some sun. And with some sun, they'll grow for you better and faster. As to not removing any of the old soil, some feel that it is better to remove oil soil because the two types of soil (old and new) may dry out at different rates. I didn't remove the old soil from a ZZ Plant I had and while the new soil dried out faster, the old soil did not and it eventually rotted on me (okay, this is maybe the worst case scenario here).
I believe (I'm trying not to speak for folks here) tarev means to mix perlite in with the existing soil (not place it on top). It won't do you any good to just have it on top, but throughout the entire mix, it will be able to "do its thing."
Planto
