2 'Roses are red,/Violets are blue/<whatever>.../<whatever>... you' is a conventional rhyme, often adopted by love-struck teenagers who aren't great poets.
3 Don't be too quick to suspect there's been a typo. This song has been sung many times, and singers with a Hispanic background may well say 'Luck' - a Spanish girl who used to wish me good luck every morning used to say ¡Suerte, Bob!. (But "Luck, may god bless you" isn't idiomatic.)
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