As well as a plan "A," a plan "B" is also advisable, in case you decide on a major project and later down the line (in my case thirty-odd years) you change your mind.
I built this 3000 gall 5ft deep koi pool (by myself) in 1986. This was its last summer, 2018.
At the time my wife worried what we would do "with the big hole" if for whatever reason I gave up keeping koi.
I said "I have a plan B."
This was it. The pool developed a leak in 2019 and I considered it involved too much work to change the liner. I got a firm in, as I didn't fancy barrowing in the 20 tonnes of eco-friendly hardcore it took to fill it at the age of 79.
This is my idea of gardening now.
To get through the base of your pool you need to get hold of one of these I have. I drilled a lot of holes through the concrete screed base before it was filled in. Any rainwater quickly disappears through the loose laid paving.