GDAE unison strung, because I'm not inclined to change my mandolin/tenor banjo/fiddle (ie, fifths) fingering instincts. I don't personally like octave strings on the zouk because they trespass a bit on the range of higher instruments, especially anything carrying the melody, and as others have said, a 12 string can do that job too (& I've a decent 12).

If you change from one stringing to another, the nut slots will need changing, and maybe a general set-up will be required. Any instrument with octave courses needs some consideration for the fact that there will often be different strings in a chord at the same pitch, and due to intonation variables, maybe not closely tuned. Some like that sound, others not.

To work on that stretch issue, capo up for a while, but slowly start capoing down until the open position stretch feels okay.

In a perfect world, get multiple zouks and have every option available.

Peace, Mooh.