It seems to me that this is a good idea, but for the pool you need a lot of space, this is an extra rent, so I wouldn't do a pool. A massage room is a great idea. Instead of a sauna, I would install a cryosauna, here https://cryomedpro.com/ you can find out more about this. I visited the cryosauna several times and I can confirm how it affects the skin, relieves fatigue after training, relieves pain if the joints are inflamed (many athletes have knee injuries and this will be a salvation for them), this is a great way to rejuvenate in a couple of minutes.