You can use the tanks... just make sure NO LIGHT gets in... don't want no "stuff" growing in them roots.

The main problem with those tanks is "drainage".

Where will they drain?
That scratches out soil.

And hydro... you can use them, but every connection will have to go through the top, as you can't "drill" or "cut" those tanks.

Get some fishies for the turtle! Turtles like fish... hehehe... (don't buy expensive fish... as they WILL end up as turtle food)