I have video in the can but currently little time to edit so I though you might like to see some progress. The other 3 (2 cutaway 1 bling) are still in the fitting stage...
8 seems the maximum 6 ideal. The repetition is not onerous. Yesterday when I got to the fourth neck the total carve down to finish sanding was taking just 30 minutes with the heel carve going very quickly. I did one time have a batch of 24 ukes to make for a Japanese company - never again... far too much of the same tho it's where I learnt how to carve necks consistently!
The wood is koa - I'd say that 2 of those middle 3 fall into the category of 'chocolate' koa with their deep browns , swirly curly ppatterns that you can't see too well. We often think of koa as being one thing but it is infinitely variable.
Busy - this is aprt of a 20 uke process at the moment with another 15 in the pipe... I think one of these in the photo will be up for sale