Is there a maximum energy for a single photon?

The wavelength, with decreases with frequency, probably cannot be less than a planck length, which limits the energy of a photon.

I've never heard of any upper or lower limit. I guess the universe has an estimated energy content, which could translate to the frequency of the ultimate photon ( it could be called the "note of creation" - the message from the beginning to itself, of which we are a tiny piece. )

Too early in the morning for this sort of stuff. Better get breakfast.

The answer depends on the frequency (wavelength) of the emitted photons. So I won't deal with numbers. Change in momentum of ship = m*delta(v) = 0.001mc = total momentum of photons emitted = Nhf/c. Solve for N.

Given our lmited experimentation devices most of all our own perception or experience itself, I don't see how we would know but sometimes I think it is whatever it takes to balance the universe or everything as a whole ( which we cannot conceive ) and to try to create that in smaller isolated incidences would not come even close to reality itself whatever that is.

No, I don't know that there's any theoretical limit.