Since Tesseract is a command-line application, it might have been coherent to recommend the use of command-line tools in the preparation phase. That way, the whole process could be more automated.

Scanning using SANE command line front-ends :

• scanimage
  
• scanadf (manages automatic document feeders)

Image preparation using Imagemagick :

• Use mogrify to convert from color to greyscale
  
• Set threshold using mogrify with the --white-threshold option
• Convert to black and white using mogrify with the --monochrome option

Actually you used Imagemagick in your 'convert' command-line - you should have mentioned that, and while you are at it you can go all the way and avoid using Gimp entirely. Less fiddling with the clickodrome, more automation !