Definitely consider the spacing (tooth differences) between the rear cogs as well as the total range of gears.

If the terrain is not extremely hilly, then you'll likely find yourself using just 2 or 3 gears in the middle to lower end of the range for up to 50% of the time (any time the gradient is close to level) - if those gears are spread wide apart then you might often end up between two of them, either pedalling with a cadence slightly too low or slightly too high.

I once made the mistake of using a SRAM 11-28 10-speed road cassette for a few days of touring. I spent a huge amount of time in between the 19 and 22 tooth cogs (a 16% difference), not finding a happy cadence. Now I won't tolerate anything more than a 13% difference between cog sizes (largest / smallest), and preferably less.

So, estimate your cruising speed (about 20 kph / 13 mph) and your preferred cadence (80 rpm for many people, 90 rpm for me) and figure out what gear ratios you'll likely need most, and look at the spacing between those to choose your cassette. Also, don't go with a double crank that leaves you in either the big-big cogs or small-small combinations, because then you'll end up needing to shift on the front way too often (this is a big problem with road compact doubles). Once you've got your cruising gears sorted out, then figure out how big of a range of gears you need to choose the inner and outer rings.