I like your Kyrie adaptation. Retention in the English version of the RE used for the third syllable of "eleison" in the source initially struck me as odd, but it may have been a good idea. Your version "sings" well.

The version of this Sanctus melody given in the Graduale Romanum is seriously flawed. The first note should be TI, not DO. Winfred Douglas used a corrected form of it in his adaptation, which is accessible on this site. (See his Ordinary of the Mass settings).
I prefer your placement of the caesura in "Heaven and earth * are full of your glory" to his ("Heaven and earth are full * of your glory.") Your placement does, however, make the task of adaptation harder. Retaining all the notes of "Pleni sunt caeli et terra" for "Heaven and earth" is not something a medieval chant composer would have been likely to do. You need to do some judicious pruninig of this phrase, relying on your ear as much as on anything else. I prefer "Blessed is he * who comes in the Name of the Lord" to "Blessed is he who comes * in the Name of the Lord," but ideal placement of the caesura in this phrase sometimes presents insurmoutable challenges. Douglas used "Blessed is he that cometh * in the Name of the Lord."

I think that in the phrase "have mercy on us" (Agnus Dei) the accent belongs to "on" rather than "us." I suggest, therefore, that you reconsider giving so much musical weight to "us." I would set "have" to DO-LA, placing the accented syllable of "mercy" on FA, where the accented syllable of "miserere" falls in the Latin version. I would then set
the second syllable of "mercy" to SOL-LA and treat "on us" as "no-bis" is treated in the Latin.