I just looked at the plans again:
The sauna in the basement would bother me. After a sauna session, you can never really go outside to "air out"; at best through the garage... but that's not really an option. A shower would be enough to rinse off after a fitness binge (or tinkering with the cars). You would have gained the space for storage instead of the sauna. I might also make the fitness area smaller (since the sauna is gone, no need for lounge chairs anymore) and treat myself to a small workshop, even if just to have tools readily stored. I miss that here too.
Then put the sauna upstairs in the private floor. Swap the bathroom and bedroom, carve the sauna out of the dressing room and then you can use that wonderful roof garden after sauna sessions. Put a few loungers there and bask naked in the sun after the sauna, very nice (as far as I see, the roof garden is not visible from outside, right?) In winter, you can get comfortable in bed and enjoy the view there. The roof terrace is big (and if you only sleep and dress up there, it probably won’t be used a lot), and I would probably also treat myself to an outdoor shower and possibly (if the statics allow it) even a plunge pool up there. Maybe also consider integrating the sauna as an outdoor sauna on that roof garden, then the dressing room can stay as is. I think an outdoor sauna is great!
For the bathroom, I would definitely go to a good bathroom planner again. As it is now, it works, but I think it’s absolutely not appropriate for the house. You can do so much more! There are such fantastic bathroom solutions, I wouldn’t let anyone build me a run-of-the-mill bathroom in such a great house.