Can I ask where you're located? I think you'd be better off first finding a trustworthy dealer than can provide some quality control and preferably do a decent setup. If you can find that, the exact model is of lesser importance
I'm not familiar with that brand but 5mm is incredibly high in my view. I prefer closer to half that - 2.5mm - which means you'd have to take 5mm off of the saddle. YIkes. How is the action at the nut?
that's not how I think of these tunings. I treat them as a transposing instrument. I always "think in C" in terms of what chords/notes I'm playing even if the uke I'm holding isn't GCEA. This means I might have to rewrite my chord chart to fit but I don't have to know different names for the...
I've started whipping out my iPhone when I find something I like. I'll even just say the fret locations like "4 6 7 0" (or whatever) so I can find it again later. Now I have a bunch of things recorded, most of which I'll never come back to 🙃
It's 16" scale. You should be able to use either depending on your tension preference. I think my 16" Cocobolo has concert strings at C tuning (but one of the last Southcoast sets so hard to say definitely) . I bet tenor strings at B tuning would also be nice