Dave, probably a very good idea to stick around and get more feedback.

In answer to your quesion, a mandolin is not the same as a guitar. A mandolin is a smaler and has 8 strings (in pairs) and is tuned GDAE. A guitar (forgetting things like 12 strings) has 6 strings and standard tuning is EADGBE.

Although playing open chords in G is easier on the mandolin than on the guitar, I think that there are far more open or first position chords available on the guitar and would suggest that for using an instrument to accompany voice, the guitar far more flexible instrument. I do play mandolin but mostly use it for single note melodies.

Jon