The Solo 610 is a single-channel pre-amp, so I am assuming you will lay down a guitar track first and then add a vocal track in a second pass. I'm also assuming you are recording the guitar via a microphone (the 414?) and not via the DI input of the 610.
The answer to your questions are yes, the interface quality does have an effect on the sound, and no, Garageband used as a straight digital recorder does not have an influence on the sound, although use of effects and other non-linear processing would.
Do you already have an interface, or are you asking us to suggest ones you might consider? If so, we need to know what sort of budget you are working to. If you are going to be tracking vocals while listening to the replayed guitar track, you will need closed-back headphones and an interface that at least has a headphone output as well as line inputs.