A few caveats, the setup Doug has used, and me too but with Gevenalle shifters, is with 9 speed stuff. When you get into 10 speed, you start getting into tricky details of shifters and rear derailleurs that won't work with each other, mountain bike stuff is "dynasis" (could be mispelled) and road brifter shifters have different cable pull.
there are numerous brifter setups that can use large cassettes and some doubles, but what you want to look into about gearing is using charts that calculate "gear inches" of your gearing, specifically your low gear.
but until you 've ridden with a bunch of stuff/ weight on the bike, in hills, all day , it's really hard for you to get an idea of what low gearing you need.
The old recommended range of 20-100 gear inches is still a pretty good one and covers a good range of touring and touring weights.
Off road or places where you'll encounter steeper hills and looser surfaces, it's nicer to have lower gearing.
and to repeat again, there's never a downside to low gearing, you might only need your lowest gear a few times a day, but when you do, it's great and you save your legs. Especially if you're having an off day (you will) or hungry and you hit the always present surprise steep bit here and there.
Sheldon brown gear calculator
html gear calculator
both good and allow you to play with numbers, here are two examples of bikes of mine