What was the focal point of the building in most central plan churches

Central Dome

Explanation:

Most churches are constructed and planned to ressemble a giant cross and where the lines of the cross intersect they almost always put a dome above it, most catholic churches from old times are planned and build like that, with two altars in the sides of the cross dedicated to diverse saints and the main altar in the upper side of the cross, with a giant dome in the middle.

this musical excerpt is an example of piano volume. (true) !

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 !