Body state after enlightenment

Ultimately everyone has to die due to ageing and/or diseases. The body disintegrates. There is no alternative whether enlightenment or not. Why is this so ? Because body is conditional and has a origin.
Body is not me , mine or myself.

One bears it like a cow wearing skin which where patched on again after it had been seperated from the body. That is what the Buddha told in regard of all aggregates, good householder, and they will go along with their nature.

[Note that this isn't given for stacks, exchange, holding on bodies, or other world-binding trades but for and escape]

The Buddha lived till the age of 80, which is 45 years after his enlightenment, according to tradition.

Based on the Pali Canon, he seemed to have lived a mostly healthy life and only suffered from dysentery a short while before his death.

From the essay "Footprints in the dust: Buddha’s travels in India" by Ven. S. Dhammika:

In the famous Mahaparinibbana Sutta we know that he went from Rajagaha to Kusinara via Nalanda, Patna and Vesali, a total distance of about 300 kilometres.

I think to travel 300 km on foot, he must have been quite healthy.

Similarly, his disciples like Ven. Sariputta and Ven. Moggallana were arahats and also seemed to have lived generally healthy lives.

As far as I know, enlightenment does not have a detrimental effect on the body. Of course, they are no longer attached to their bodies, so they may not lovingly take care of their body, looks and health in the same way non-enlightened folk would. They would follow the Middle Way in taking care of their health i.e. neither extreme asceticism, nor indulgence and vanity.

Ageing, disease and death affects all sentient beings, regardless of whether they are enlightened or not. All conditioned things are impermanent (sabbe sankhara anicca).

As far as EBT (early buddhist texts) go, I'm pretty sure there's nothing to support any of your ideas on what happens to the body of any arahant after nirvana.

There is this SN 47.9 Gilāna sutta, where the buddha is close to death but prolongs life, and limits body pain with animitta samadhi, but not all arahants could do that. Otherwise his arahant body after nirvana (while alive) seems to be just as frail as any normal human:

I’m now old, elderly and senior. I’m advanced in years and have reached the final stage of life. Āsītiko me vayo vattati. I’m currently eighty years old. Seyyathāpi, ānanda, jajjarasakaṭaṃ veḷamissakena yāpeti; Just as a decrepit cart keeps going by relying on straps, evameva kho, ānanda, veḷamissakena maññe tathāgatassa kāyo yāpeti. in the same way, the Realized One’s body keeps going by relying on straps, or so you’d think.

And there are the suttas where the Buddha and Moggallana say had they chosen to, they could have extended their lifespan for the remainder of the aeon. But this has to do more with supernormal powers, which arahants may or may not have developed, it doesn't have to do with what happens to everyones' body after nirvana realization. The EBT's AFAIK don't explain how that ability of remaining for an aeon works. Theravada commentary (which I disagree with) says that 'aeon' is to be taken figuratively as being able to live out a natural human lifespan (100 years or so). I suspect what that power to live out for a remainder of an aeon really means, is living out the aeon in a ghost state in a mind made body (for reference, a lower brahma realm has a lifespan of one aeon). There are accounts of taoist masters doing something similar, not yet taking rebirth in their next form, but hanging around in some kind of intermediate state with ability to communicate with their disciples in the human realm.

Regarding the ability to sleep less, nor not sleeping at all and remaining conscious all the time, the EBT's do mention some things regarding that, but nothing specific only for an arahant.