That sounds nice.

They all sound very beautiful, although two things jumped out to me as slightly unusual. Unlike a Gloria, an Agnus Dei often seems to end a bit more subdued, more of a gentle resolution, since it is right before Communion. A crescendo in that spot seems odd to me, but that's just my opinion. Also, the Benedictus is usually a separate movement from the Sanctus, sung after the elevations (at least at EF Masses) I don't know if it's a hard and fast requirement, but every polyphonic Mass I've ever seen has them broken up.

I'm curious what your method is to get such nice sounding pieces. Do you figure out the chord progression first? Where do you start at when you sit down to compose something?

I am somewhat perplexed by the plethora of parallel fifths in these movements, whereas the preponderance of composers tend to eschew parallel fifths, even when composing in a modern idiom (except perhaps purely atonal music). So I'm curious whether all those instances of parallel fifths are deliberate or perhaps simply overlooked.

The effect (at least to me) of a parallel fifth is one of weakness of (harmonic) texture, especially when it occurs at a cadence (such as the end of the Agnus Dei) or at a transition such as that from the last syllable of "excelsis." into the first syllable of "Benedictus" in the Sanctus.