1. If you started the opening soprano pickup with a Do-Re eighth note slur, it might have a touch more continuity with the beginning of the second half of the song. 2. I might suggest changing the first chord in measure 12 to a vii chord instead of the IV. It would prevent the V – VII progression. See attached suggestion.
I like this! The only issue I see is that “Sol-Fa-Re” at the end of the first phrase isn’t an intuitive soprano line. I’d change it to “Sol-Mi-Re” if possible, which also reflects what happens later in the song. It would necessitate harmonic changes, though.