1) Every track in a pattern can have either normal data (keyboard playing) or samples.

That is correct. The ISS always places MIDI data on a track. MIDI data can be either normal keyboard playing or in the case of an audio sample, a Note-on event that triggers playback of an audio clip. The ISS (sample+note) places the MIDI Note-on event precisely at the punch-in point, and creates the Note duration (Gate Time) to hold the Note precisely to the point of punch-out (or where you stopped sampling). This recreates the same result as if you were actually recording audio to a hard drive, but in fact, you are creating a sample with precise timed duration based on sample in and sample out points.

In other words, no audio is actually recorded to a track. When you look at the event list of the Pattern Track you will see a MIDI Note-On event with a duration that represents the precise length of the audio sample. The integration of the sampler with the Sequencer was the core concept of the Motif series.

In order for the sample audio to play, the Note-on event must trigger the audio... so unlike an actual audio track *where* playback begins is critical. The Note-on event must be activated for audio to playback (you must start from the top of the audio clip — starting in the middle is not possible, it’s a “sample”). Each KEY can hold a different audio clip. So for example a Drum Loop could be assigned to C3, a Percussion Loop could be assigned to C#3, and so on ... each of the 128 Keys, in theory, could house a different audio clip. In practice you would group them so they could share the same effects, EQ, etc., etc. remember if they are all on the same Track you lose the ability to Mute one of them individually - if you see what I mean.... mute the track all the audio clips on that track are muted, so decide based on what flexibility you require.

So you could have Section A use C3 as a looping phrase. Section B might use the same User Sample Voice with its looping Phrase on C#3...

2) I must turn on Phrase Header so that every unique sample on every track within a pattern gets its own number -that way I can record different samples in different Sections using the same track number.

Correct again. In practice, the ISS automatically creates the Phrase Header, but you can edit it as necessary... by placing the Pattern in Record Standby and using the [Function] button to update the contents of the Phrase Header.

3) the 1st sample audio I record (say on Section A, Track 16) will be run for 2 measures which is the same length as the section. It will be numbered User Sample 1. The note--on MIDI keybank defaults to C3 to trigger the sample.

Correct... What is critical here is the difference between Phrase Length and Pattern Section Length. The Section Length when longer than the Phrase, the Phrase simply repeats to fill the length you allow the Section to play. Go to the Pattern [PATCH] screen, the Phrase Length is shown on the same line as the Track. Phrase Lengths can differ from Section Length...

4) I want to copy this same User Sample 1 to another section within the same pattern, say Section B. Couple questions here;
a) Do I (must I) keep the C3 Note-on keybank to trigger this same copied sample?
b) If the destination (Section B) happens to be longer that the source section, say eight measures, can I have this same two measure User Sample 1 loop (4 times) to fill the eight measure destination section? Do I still record start - stop as two measures or eight?

If you want the same sample to play in any other Section simply activate the Phrase in that Section. You can do so on the [F4 PATCH] screen... simply select the Phrase by Number. Because the data necessary to make this phrase play is contained in the Phrase Header, when you activate that same Phrase number in Section B it will play the correct sample, if Section B is longer than Section A, the Note-on that triggers the phrase simply retriggers the Phrase, appropriately.

5) Next I want to proceed to sample a second piece of audio within the same pattern;
a) Can I choose any empty track within my desired Section, or does all samples (within the same Pattern) need to remain on the same Track (I would think it doesn't matter, correct)?
b) Must I always assign a different /unique keybank trigger note for EVERY unique vs copied user sample?

Correct it doesn’t matter, it is up to you. If you wish to add additional sample to the same Track make sure you target a different Key (C#3) and create a separate Note-on event to control it.

Hope that helps.