How many octaves would you have to add to a guitar to reach the octaves of a mandolin? Like how many strings and frets would you need to basically stick a mandolin into a guitar body but still be able to play the lower octaves of a guitar.
The high e on the mandolin is an octave higher than a guitar, so it depends on the mandolin, they have anywhere from 15-29 frets. If it's a 29 fret mandolin, it would be 15 extra frets past the high e7 on the 24th fret of the guitar.

Mandolin is tuned GDAE, low to high, not like a bass, the letters are reversed. The low G is the same as the open G on guitar, and as I said before, the high e on mandolin is an octave above the high e on your guitar. It's tuned the same way as a violin, in fifths, as opposed to fourths (primarily) on guitars and basses.