Hi Mikey. For vocal and guitar I use the Apogee Duet which is designed for Garage Band and Logic on the Mac. It has 2 instrument inputs, 2 XL Phantom power mic inputs and two speaker inputs plus 1 Headphone jack. These are on a break out cable firewire to my Mac. My Roland E60 keyboard is connected to with MAudio USB Uno midi cable. The Apogee is not cheap but the sound quality is fabulous.
P.S. I assume you got the Gretsch. I just got an inexpensive Squire Custom Vibe Tele and its a riot going through the different effects/amps in Garage Band and Logic.
Hope this helps.
Brian