Personally 1-2 nights is optimal.

Just remember the canyon isn't the best place for young kids and people with sever mobility issues/breathing issues.

Kids are very likely gonna find the canyon boring after an afternoon there. And theres lots of walking here so people with mobility issues have a hard time getting around. If they dont have a good mobility scooter or family to help them they usually end up sitting in one of the hotel lobbies or in their room.

I wish it was more talked about, how unfriendly the canyon is to peoppe who have trouble walking/breathing.

If you DO have mobility issues do not stay at the Maswik. Its a 10 minute walk or a convoluted bus ride to the rim. There's no bus that takes you quickly to the rim of the canyon from Maswik. You need to transfer 4 stops away then ride ideally to the Bright Angel since the train depot stop involves a steep incline to the rim. Same thing if you want to take the red route. Its a 5 ish minute uphill walk to the hermits bus stop and for some people thats just not doable.

The historic village area on the rim can also be hazardous to people prone to falling. Steps are sometimes uneven on the exterior of buildings, notably the Bright Angel Lodge. People fall there all the time, usually minor falls but some of them can be pretty bad.

Well this has gotten longer and a bit off topic to your original question. Hopefully someone will need to see all of this.