This is going to be really complex, as it's not something you just jump into randomly some day with the expectation of pulling back perfectly readable code. Understanding programming concepts is really important, and understanding low level data structures is even more, but you are wanting to go pretty low level.

The basic answer is you will not get 100% correct human readable code as aspects of the code are lost during compilation. If you really need something analyzed it is best to hire someone who has done reverse engineering on embedded systems before. Windows RE Analysts may work, but only a select few as pulling apart embedded systems and microkernels is much different from pulling apart windows binaries. 

It doesnt stop you from understanding it, but there can be tar pits in some areas.

I RE embedded systems everyday and I pretty much use a handful of things:

Primaries: IDA PRO and GDB

aside from that I use a hand few of custom tools and a lot of python.

There really isnt any book I can give you, and there really isnt an order. First I would read the book "Real time concepts for embedded systems" Then I'd read the book for the microprocessor the device runs on.

Aside from that it just takes a lot of doing and a good support team. There is not much info out there on REing embedded systems so having people to goto for questions is essential.

Keep in mind though, RE work is resource intensive. A single person with 5 years of experience, who works on a small device can take between 3-12 months to RE the device depending on the objectives.