That is definitely a gray! You must have more than one living around there too, because only the males call, the females are quiet.
As for the other questions, I've never raised tadpoles myself, but MANY here have and can give you some good advice. A 5 gallon planter seems quite small for a load of tadpoles though. Also, keep in mind, if they get in your pool, they will die. The chlorine will kill them or they will drown.
I had tadpoles (toads) for about 3 days before dumping them in a pond where my kids found them, obviously that isn't an option for you though! Good luck, I hope someone can help you out.