I think it is nice, with two exceptions as to the format. First, centering always makes things hard to read. Just left-justify and indent both sides, possibly controlling the line breaks yourself so your paragraphs don't wind up with a dinky little last line. Second, the four medallions of the evangelists are both too small for that level of detail, and also thematically bizarre, since altar boys (and these prayers) have nothing really to do with the Gospels.

Also, as you may have noticed, the vocative "O Lord" is not a proper translation of the nominative "Dominus." Douay-Rheims adds the understood copula and renders this line "The Lord is the portion of my inheritance and of my cup." (Chuckling at "cup" for "calix"; that'll make somebody blow their stack.) The second "of" is very helpful here, to make it clear that it is not to be understood as "The Lord is . . . my cup." And for that matter, in the surplice prayer, "by God" is a pretty poor translation of "secundum Deum." The D-R, again, (Eph. 4:24) properly gives ". . . who according to God is created in justice and holiness of truth."

I'm not sure if the vesting prayers are where you want to try your hand at dynamic translation. :-)