Well, take the first few measures (this is what I hear, roughly):
The chord progression seems to be: Gm, Dm/F, Edim, Fr+6, Bb/D, Adim/C, GM/B, D(/F#, then D). These harmonies form a progression of harmonies based more on the linear motion of the bass (its stepwise descent) than a traditional pattern of functional harmonies. It would seem that the primary structural harmonies (according to Classical-era traditions) are those at the beginning and end of the passage, I (tonic) and V (dominant). The other harmonies are linear harmonies, embellishing chords that are formed by linear (stepwise) patterns in the bass (and other voices). These chords don't always fit into the three functional categories we discussed (vi should be a minor chord in the tonic category, for example, not a diminished triad); nor do they necessarily follow traditional functional progressions (predominant->dominant->tonic). In this piece, then, the Dm/F would appear to be a non-functional minor V chord, the Edim would be a non-functional diminished vi, the Fr+6 doesn't fit into any functional category (predominant, dominant, or tonic), the Bb/D chord's primary function is to connect other linear harmonies (although, as III in the minor mode, you might consider it a tonic chord), and the Adim/C harmony (a iio6 chord) doesn't resolve to dominant harmony as it should, unless you consider the GM/B to be an altered version of a cadential 6/4 chord (a purely embellishing harmony that resolves to V at the end of the phrase). And yes, the F# in m.4 would lead to G (in the next measure), since it acts as a leading tone within dominant harmony. Hopefully this helps?