I play in a band and we do fly out dates (casinos, festivals, etc.). We use backing tracks and I mix them and convert them to MP3's on my desktop using Sonor Studio 8.5. We try to have the FOH guy record the show onto a USB or Ext HDD. I don't want to record any live performances onto the laptop just run the backing tracks and edit the FOH USB or Ext HDD recording. I'm thinking of buying Sonor Artist, and a laptop, and loading Artist on the laptop and putting the backing tracks and editing the FOH recording in Artist. It doesn't seem to me that I'd need a very powerful laptop to accomplish this "lightwork". Any thoughts or suggestions?

I think any current laptop should be able to accommodate this.    
 
Really, the big drain would depend on whether you're recording two tracks from the FOH or individual instruments.  Either way, recording a dozen or so live tracks (with no onboard FX etc running) should work with a std laptop with 8Gb of RAM.

Most larger acts using computers for backing tracks have some redundancy built into their setup in case one fails during a show. A second laptop is synced or locked to the first and will continue in the event that one fails. The audience will never know there was a problem.
I couldn't tell you how they do it specifically, I would guess it's some kind of a midi sync with both computers fed to a mixing desk.