Any good reference works on serial buses?

Asynchronous and SPI are dead easy -- any UART data sheet will pretty much give you all you need to know for asynchronous, and the data sheet for any SPI block in a microcontroller will give you what you need for SPI.

I2C is harder, but can be fairly easily bit-banged in a microprocessor, if you don't mind going slow.

CAN is harder yet -- you're into "buying IP is better" territory, unless you have some serious sales volume. Ditto USB, although I know of some bit-banged USB examples on microprocessors (bit-banging USB is kind of my personal gold standard for easy -- if a hobbyist can bit-bang it, then it should be easy for you, unless they're ignoring all sorts of corners in the "real" spec).