You need to plan on how your peg head and those tuners are going to work with the pair of strings. It's really easy to get their placement wrong and one string rubs / rides on the other's post.
Have a clear idea of what strings are going to be used as well. If it's unison high g's then the nut and saddle spacing might be narrower than say an octave pair.
I've built both octave G's and C's in 5 strings. You can accomodate both by carefully planing the bridge, and offering 2 nuts to the client. Then they have the option to try different combinations of strings.
You have to use either a string through bridge or a tie bridge. No room to use bridge pins unless you make a very deep bridge and stagger the pins. Not a good look on a uke.
Other than that, have fun with it.
