Timmie, sorry it's time to permanently close the pool

You will want to 'poke holes' in the bottom of the pool before adding the fill material. You don't want the pool to float up once it's filled in! Let any water that enters where the pool was or any water that might try to collect under it be able to find its equilibrium level.

Not that I know a lot about this, but if it were me, I'd put the concrete from the deck into the pool, then fill with sand or unscreened fill and have ~ 4" of top soil. Of course, you'd want to tamp or wait for the base material to settle before adding the top soil.

As you'll need to buy the top soil, decide what you want to grow there and talk to someone who 'knows this' to see how little you can get away with (I believe that grass only needs 2" )