Hi Matt! I've read your lesson and managed to do some cadencial 6/4. I think we can go on, too.
In the bar 18 of the sonata there is an imperfect cadence (ends with G major). After that the next phrase(?) starts with a G major chord, too, and in bar 19-20, note F is not used. Bar 20 has a C major chord in 2nd inversion perhaps to avoid a cadencial "feeling" (V-I6/4 is not a perfect cadence), however I'm not 100% sure about it.
Bar 21: There's a D major chord in 1st inversion (F sharp in the bass) with an added 7th (C) at the end of the bar which suggests a modulation to G major (bar 22). At bar 23 a 7th (F natural) is added to the G major chord, and it modulates back to C major (bar 24).
Hope I've answered correctly. It's a pity I cannot play it on the piano
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I like anything in 3/4 time; this piece of the sonata can be very happy
