How large or small can frequency in the EM spectrum get? The largest frequency range is gamma rays, but does the EM spectrum 'stop' somewhere? Like is there a limit to how large a frequency can get?
Or how small frequency can get?
Is it one of those things that theoretically nothing is stopping it, but nothing in the universe can produce ways of such a frequency or beyond a certain limit?
Does light from galaxies redshift to the point where the wavelength is just insanely long? Long enough that we can't see them?
 A: I'll start with the second of your questions. Yes, light from very distant galaxies gets redshifted to such long wavelengths that there practically isn't any light to see. The lower limit on frequency is zero. Obviously. Technically one could say there is no signal at $0\,Hz$, but that still put a lower boundary on the frequency. Objects on the edge of our cosmological horizon have their light redshifted almost infinitely by the time it reaches us.
As for upper bounds on frequency, there's two ways to think about this. Strictly speaking, there is no limit on how high a frequency can be. I could say the limit is that wavelength can't go below zero, but that would feel cheap and like cheating. A photon can have an arbitrarily high amount of energy. However, something else to consider is the limits on knowledge of frequency. If the wavelength goes below the Planck Length, we really don't have any measurement equipment that could theoretically ever measure it. Not only that, but the energy of a photon with this wavelength would be at the Planck Scale. At this scale, the Compton wavelength and the Schwarzschild radius of a Black Hole are about equal. That means any photon with this high a frequency has enough energy to spontaneously create a particle that immediately becomes a black hole and swallows the photon. This indicates two things: 1) We really need Quantum Gravity to adequately describe this energy scale and 2) we can be pretty sure that whatever is flying around with this energy is probably not photons.
So a lower limit on frequency is zero and an upper limit is that with a wavelength of one Planck Length. (At least, that's the upper limit until we find a nice theory of Quantum Gravity).
