To pleat to the sett or pleat to the stripe, that is the question

[chasem]

1 - do the pleats crease at the same stripe in every sett or is it every other sett? [there are two setts in this tartan]

Typically, same stripe in every sett. Your tartan doesn't actually have two setts, there's one sett (note the double-stripe centered in one block of blue, and two double-stripes -- one on either side -- in the other block of blue). However, there are two light-blue stripes per sett, so it could be pleated to every light blue, or every other, most likely depending on the size of the sett.

I'm actually making a kilt at the moment out of Forbes (similar to the Polaris) with a 14" sett. There is a white stripe every 7" though, and I'm pleating to every white stripe, rather than every sett. Either way works.

2 - do the dimensions of the sett make a difference? [sett dimensions of my swatch are approx. 4.5" x 5.25" - not sure why it isn't square]

Sett dimensions will determine the size of - and how many - pleats.

3 - does the outer edge of the pleat align to a stripe on the underlying pleat? [this seems improbable simply because when the kilt lies flat on a table the pleats are tapered - but I need to ask anyway]

yes and no. The top one-third of the kilt it won't line up with another stripe, as you said, both pleat edges will be tapered. The bottom two-thirds, however, are straight down, so the pleat edges will be perpindicular to the selvedge (will line up with a stripe if there's one there).

4 - does the kilt wear differently from one pleated to the sett? [I very much enjoy feeling the kilt move as I move]

Nope, the pleats will be done in the same manner, so the kilt will wear just as well either way.