From what little I know they say that a 10 gal tank in the right size for them. How long is your guy, full size they get about 10" to 12" long. Meaning that it should not stunt their growth, but a biger tank is always nice.

If you do go with a bigger tank, you do know it has to be a established tank already, where the nitrogen have cycled. As for the air pump, I'd keep it running all day, just get a small one.

I'd also go with all gravel, it's just safer in the long run for him. Really the clean up wont be that bad in a 30 gal tank, it might take you a min or so longer then the 10 gal.

As for the heater, I don't know if they have ones that sit on the bottom but I'd go to Drsfostersmith.com if it's out there, they will have it. I find all kinds on things there they I don't find other places. I have heard of heaters that attach under the tank and heat it through the glass, but I just not sure about them. I know they use them on Iguana tanks.

Just wondering but with the water so low doesn't it stay warm enough at room temp. I belive they only need the temp between 60 and 75?

Chemicals on a 30 gal is no more harder then a 10 gal just a little bit more of them.

Putting the aquatic frog in with him, might work but I'd watch them for a while. Aslo make sure that the frog wont add any ammonia to the tank that you don't want.

I hope I helped some, but I was doing this all from memory, so I could be off some. But I am 100% sure that you need to established your tank, thats so important. But I bet you knew that already.