Theoretically, there is no reason why there should be an upper limit to the energy of a photon. However, in real life a limit is that the amount of energy in the universe is finite and limited – and so this would be an upper limit.
No, I don’t believe that there is. However, I don’t think the photons could go very far when they have very high energy, because they can turn nothingness into something. Completely empty space is called a vacuum, but with photons of high enough energy, the vacuum absorbs the photon and can turn into a differnt type of space! Very strange, I don’t really understand it.