RE: Inches to milimeters
You can substitute the closest size wood with no problems. I was stationed in Germany for a few years and ended up with a large stack of metric wood. I keep it separate from my other wood, but I use some of it in most models I build. I just make sure I make symmetrical parts from the same wood.
In other words, if I sheet one aileron with 1.5 mm then I do the same to the other.