Yes, you can do this. Your suggested setup for Input 1 and Input 2 is correct (or you could reverse them). Here's a preset that might help illustrate the basic setup. It was created for a setup pretty much exactly like you describe.

http://line6.com/customtone/tone/215659

The differences might be that the Inputs are reversed (not important) and the FX are (if I recall correctly) all in one path or the other. The most important point is that there are NO FX before the path split. This ensures that your vocal and guitar signals are processed completely independently. If you want them to share FX (e.g. reverb) you could simply move that FX to a point after the mixer so that both signals pass through the reverb FX.. But I would only do that if I ran out of FX slots; otherwise I would keep a reverb FX separately in both paths for independent reverb control.

Both paths are stereo - meaning you could, for instance, use a stereo delay on your guitar (as long as you don't place a mono FX behind it in the signal chain). You can use the mixer to pan your two signals as you desire. If you are feeding into a mono source (your power amp?) you can just use one of the unbalanced output jacks - the signal will be summed to mono.

Hope this helps.