It's likely not as great as you think. I've done this for work and it is very workable. But, the hotels that are willing to cut you a deal are often not in bad areas, but not the prime spots. So maybe close to downtown/beach but a bit of a walk. Your beach front hotel can charge a big premium in season and they don't want to give that away.
It also puts you on all eating out food. If there is something like a Whole Foods with a salad bar nearby maybe this is workable, but not cheap. Or there is a good chance you will gain some weight.
A lot of hotel rooms have kitchenettes, especially in cheaper hotels, and those ones also often have free breakfast. If you were a one meal a day intermittent faster like me, you would be set.
I agree with this, which is another reason I think the OP would be better off going with more moderate hotels, instead of 5* places, which likely don't have efficiency kitchens in them. I'm also not sure how many five star hotels have buffets, though them do mention that specifically in their post, as "scoop mountains of food onto your own plate" is generally not five star service, especially for anything other than breakfast.
Yeah, I have no idea what 5 star means in their location.
If they're considering it, then I'm assuming it's not crazy expensive.
It would be nice to see some actual numbers to even have an opinion. For me, I get the family rate at all Marriott chains, and even then, it would be substantially more expensive for me to live in smaller accomodations than my current 1 bedroom apartment, even including utilities, internet, and paying a housekeeper.
And that's using the cheapest rate at the crappiest hotel in my city, in a terrible location.
So I would really love to hear how this would make sense financially. Also, what the motivation would be. If OP is willing to downsize that much and their home is worth that much to rent out, then why not move to a small apartment and pay for housekeeping and cooking?
They would have to cost it out, but the cost for me to hire a weekly housekeeper who also cooks isn't particularly high compared to outsourcing that work to a hotel.