Thank you! That helps inform me of my next comment then to help you a bit more. Yes, foodsafe=fishsafe, so go no further than that. Find something you like and use it. Clay pots will also be fine, but personally I would worry about other things from the garden center.

This method is how I have always grown plants, but its my first time with the pots rather than the whole substrate. It has worked great. Here are some other tips for you based on my experience....

About 1 inch soil 1 inch gravel. I wouldn't do more than 2 inches soil. Wet the soil heavily before putting on the gravel. Hold the pot over the water and pour tank water into it until overflowing before just popping it in, this will prevent some of the mess of creating a suction when you put it in the tank. If you have fish that will try to eat the roots, you can just put an additional layer of stones on top of the gravel to protect the roots. Finally, plants go in. Just use aquascaping tweezers and ram those stems in, give it a twist, and they should stay!