Great job, Dan! You can't go wrong with a Martin S-1. I have an S-0 (with the fretboard running a shorter span), and I love it.
Nice playing and singing! Sure, you may need to gain a little more confidence in your singing, but that will come-- just keep doing it, explore tons of your favorite songs, tinker with doing them in different keys, and gradually you'll settle into a "vocal range" that's right for you. And that's when the confidence level accelerates!
I think a great combination is to use that soprano uke, and then try to establish your vocal range in a lower register, where it's physically comfortable for your voice (unlike the old days where we sang everything WAY up there-- think Michael McDonald on the Doobie Brothers' "What A Fool Believes").
That way, the uke and your voice sort of "stay out of each other's way", and it makes for a pleasing and uncluttered sonic result. It is said that Nelson Riddle arranged much of Frank Sinatra's songs in that fashion-- lots of higher-register instruments doing the music, leaving room "down below" for Frank to do his thing.