Just got caught up on this thread- u definitely have a mess to clean up but it’s certainly doable & it sounds like you may at least have some useable equipment for now. You can always change each thing out as needed so just take it one step at a time. There are will be wait time on anything u buy so no need to let that slow your progress if you can begin with what u have.
Its also nice that u have a lead on a liner locally incase this one becomes “injured” in the clean up process or u uncover a major flaw. It may not be the best one but it is available!
Step 1- scoooooop! Draining a little more but not completely may help this process.
There are a few tools that make it easier like a wide mouth leaf net or 2, sturdy poles & possibly some teenagers

also some bleach if it makes you feel better about handling the muck. You may kill a couple birds w/ one stone if you can siphon vac debris over the side of the pool while simultaneously draining.
Step 2 - Deep clean the sand filter like in the tutorial linked above &/ or possibly replace the sand if its looking like the deep clean isn’t cutting it.
Refill & try out your equipment .
I’m keeping my fingers crossed for you

Step 3-
SLAM Process
While doing so a leaf catcher vac attachment can prevent clogs from any large debris remaining.
As for bleach-
Call around to your local pool stores & see if anyone sells chlorine in large refillable jugs- it’s usually 10-12% & cheaper per gal. As well as convenient compared to clearing the shelves of the local walmart.
The best way to eat an elephant

is one bite at a time lol.
Keep us updated as to how things progress- we

Swamp to oasis threads

oh & pics - did we mention lots of pics!