What is the difference between the steady beat and the rhythm?

The beat is the steady pulse that you feel in the tune, like a clock's tick. It's what you would clap along to, or what you feel you want to tap your foot to. The rhythm is the actual sound of the notes, which in a song would be the same as the words.

i'm not sure i completely understand your question, but i will do my best.

i think the answer you are looking for is sequence. (see below)

a repeated melodic fragment would be best defined as repetition, while repeated chords (different or the same) could be a chord progression. however, you then mentioned the chord and melodic fragment beginning on higher or lower pitches, in that case, the answer could be best defined as a sequence. the definition of a sequence is as follows: "the restatement of a motif or longer melodic (or harmonic) passage at a higher or lower pitch in the same voice."

let me know if this !