There is a nickel layer between the brass and chrome, as mentioned above. I'm not sure how much aluminum is in this camera, but it doesn't seem to be much. There are the few plastic bits, as mentioned above - tip of wind lever, battery cover, film take up tulip.
For me, I had a Nikon F3 for over a quarter century before I obtained the M7. The M7 is as easy to shoot as the F3. The big plus which nobody has discussed so far is TTL flash control. This takes out a lot of mental calculation with guide numbers (still the most reliable way to determine flash exposure).
Further, the M7 can fire just before the second curtain moves (second curtain synch), offers strobe capability (multiple flashes per exposure), and high speed flash synch with SCA 3502 flash units. I can also dial in exposure compensation into the flash unit, and have multiunit TTL control through the Metz system.