Hi Akira,
The material is called 'Chemiwood' though other names like Modlab are also used for some grades. I imagine that Renshape is a similar wood flour/resin compound that can be machined, turned etc.
My approach to the ballasting is because there isn't a huge amount of space for stuff inside because of her shallow hull and the baulks of balsa used to create the hull shape. The hull is so buoyant!
I will make the barbette traverse but the guns run up slopes on firing, so decided to keep things less complicated. More detail and less action!