As a general idea a telescope with an 8-inch aperture can be used visually for supernova searching down to about 13th magnitude. The high magnification increases the contrast with the background, making it easier to spot stellar images superimposed on the hazy galaxy. A CCD imaging camera that mounts on the telescope greatly increases the magnitude limit you can search. An 8-inch telescope can now be used reliably to hunt for 16th magnitude supernovae. Galaxy Charts and Reference Images.
Galaxy locating charts are helpful.
However, it is important for you to get reference images using your own setup so that you can readily compare images to see whether anything has changed. Supernovae are easier to detect and, hence, are more often found in bigger, brighter, and older galaxies than in smaller, less luminous, and younger galaxies. Spiral galaxies statistically produce more supernovae than do elliptical galaxies. The only absolutely sure way to confirm your discovery is to have it confirmed through spectroscopy at one of the university or professional observatories. For example, the STScI Digitized Sky Survey is an excellent on-line source.