It is hard to beat a mountain bike crank (22/32/42) on a touring bike. You would need to get the matching front derailleur. Sometimes you can get a road front derailleur to work. I think they changed the pull ratios so that road and mountain rear derailleurs are different, but I think fronts are still the same.
I think you've got that backward (unless it changed this year). Shimano rear derailers have been agnostic for road/mountain and number of speeds for a long time. My 2009, 9-speed Novara Randonnee works well with a Tiagra front and Deore rear derailer, both with STI brifters. The small chainring is a 26, IIRC, although I may get a round tuit and change it to a 24 one of these days.
There's no need for a big chainring on a touring bike. The only time you might need it would be if you take it on a fast group ride, and the bike gives you a ready excuse to drop when pack speed exceeds 30 mph.