I had a look at the Fast Track C600 and it looks like a good audio interface. It should work for what you want to do.
Connect your guitar and mic inputs into the audio inputs of the Fast Track. You can connect your MIDI keyboard either to the Fast Track or, if its a USB MIDI keyboard, you can plug it straight into the laptop.
Then in ALK, open the Preferences and select the Fast Track
This tutorial may help you:
Then create Audio (guitar, microphone) and Instrument (MIDI keyboard) tracks and in the track panel select the correct inputs. Take a look at this tutorial:
I think the perfect set up is an interface like your already have (the Fast Track) and a MIDI keyboard. There are many different MIDI keyboards and they will all work. If you want something small but useable try to AKAI MPKmini
To connect to the mixing desk at a concert, connect outputs 1 and 2 (the master left and right outputs) to the mixer:
Often at a concert the sound guy will have DI boxes to connect such a device to the mixer. To connect to the sound guy's DI box you can use jack cables.
Hope that helps! I also recommend taking a look at all the tutorials on our YouTube channel https://www.youtube.com/user/zenAudioGmbH