Welcome and thanks for the compliments!
On the build volume side of things, Z is the most important. You can do you large build for wood and knowing that you will try some aluminum just make the z really short 2″-4″.
The Z axis is the “weak” link in that aspect, because it is combination axis. The bits are usually 2″ so usually you will never usually mill deeper than that so the added height would be for material thickness. I have about 2’x2’x8″ build volume and aluminum works fine. I use the added z height for 3d printing. My next build will probably be even smaller. I want the rigidity so I can increase my cut speed. I have also never cut anything large, but that is just me.
Good luck let us know if you have any issues.