It supports different cpu architectures, e.g. ARM and X86. However, it does not support different scheduling. In fact, the different approach towards CPU locking is one of the main reasons that leading to Dragonfly BSD.
The source code is orthodox, comparing to the Linux kernel source code. It is because there are always people trying and researching different things within the Linux kernel space.
It is relatively easier to read the FreeBSD source code along with this book if you want to learn OS architecture.
https://www.amazon.com/gp/product/B00O56CFEE/
Honestly one of the most surprising questions I've seen here - documentation is THE feature that drew me to and has kept me on FreeBSD.