I switched over from a MixWiz to the XR18 in the spring. I figured it was an economical way to dip my toe in the "digital pool". I'm glad I did! Mixed all summer (about 30 gigs) with the XR18 with zero problems including the usual back pain from hauling a GigRig around.. :-)
I'll be moving up to an X-32 Rack with some SD16s soon and keep the XR18 as a backup.
1 - Yes, I run the XR18 next to the drummer, CAT5 to an external router and then to my laptop. I use the laptop and a tablet to mix.
2- I use the internal router when tweaking at home but not much else. It works and would use it as a fallback but I wouldn't want to depend on it in a gig situation, indoors or outdoors. I don't remember the range being spectacular.
3- I use all 18 channels now and 5 Aux's (was using 6 with a sub send channel but got new speakers and don't need to do this now). 5 piece band ( drums 7 channels, bass 1, guitars 3, vox 5, Ipod 2). I know I can run a very successful gig with it 16 instrument channels. I want to expand and have more channels as I do more gigs but I wouldn't hesitate to recommend the move. It takes some getting used to but once you realize the freedom, flexibility and weight savings,,, you'll be glad you did it.