Scale length is designed to conveniently allow the player to find an instrument they can physically play more comfortably, if you sing you will tune your guitar to a key in which you can sing comfortably, though different tunings offer different voices and a different feel to the music, low keys thicker strings, high keys thinner strings - decide on one scale length (very commonly 25.5", same as a Strat). (-:
consider restringing one of your current CBGs with a different string set. See if you can achive your desired tuning. If not then consider your next build with a different scale length.
Scale lenght and string selection both matter. And as the Kid says the two fit together best when combined with an optimum tuning. I have built several with different scale lenghts and string sets. Sometime you have to play around with strings and tunings until you find the combination that "works" with a particular CBG.
I prefer a 22" scale. I find that it makes the stretches between frets easier, especially using open tunings. Here is a suggestion. String using ADg strings and tune Open D: ADf#
I use a "movable chord method", so it possible to play in all 12 keys on 1 CBG.
See CD 6
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So once you pick the scale length that you like to play (me, I like 17") you then decide on the tuning you want to have. Let's say Gdg. Then you go here: http://www.strothers.com/string_choice.htm
You plug in your string length (in my case, 17) and then enter G. It tells me I need a .017. Then I put in d, and it tells me to use a .016, and so on for the little g string.
That gizmo lets you choose the best string for the scale and tuning you want, instead of guessing, or hoping or trial-and-erroring. And it is just a starting place, you can loosen them up for a lower tuning if you like to play all floppy and buzzy. But at least you are starting from the optimal.