Just caught up on this thread- so a belated welcome to tfp neighbor!
definitely get a wide mouth leaf net & scoop as much solid debris as u can off the cover - the water is definitely gonna mix when removing that tarp but thats ok . Once u get it off do the same in the pool - blind scooping is ok

The more organic material u can get out the better.
harbor freight sells mesh tarps - if you have help u may be able to finagle one under or over the existing cover to help catch the debris. If u get a large enough one you may be able to use it later as a leaf net.
You need to find out if it was a baquacil pool. Look around for leftover chemicals & report back. If it was a baqua pool there’s a specific procedure for converting to chlorine & in your case it may begin with a water exchange.