1) i started by installing a simple distro like Kubuntu and once i got familiar with the system i went on to do little experiments and projects, setting up servers and so forth. basically, you have to be a selfstarter and able to learn on your own, sure you might find some dude that knows about GNU/Linux but only now are they starting to offer basic classes in it and publish books.
basically you want to become familiar with the command line, and you can always turn to Unix for example too.
2) no. flashing Debian onto my Beagleboard and programming for it takes a totally different skill set then programming or even just functioning on your typical 80x86 or amd64 terminal. for example in most mainstream distros you can get away with scripting everything and just downloading this package and that package to meet dependencies. however on the Beagleboard, you have to be very very very careful and aware of system resources and how large your binaries are. you have to take advantage of at least some very low level features of C if not acutally using ARM Assembly. the Beagleboard is probably one of the more powerful embedded platforms too.
3) check out Linux From Scratch, just google it, they have a little guide. its a little daunting at first, but after you do it a few times (mostly failing horribly) you will learn a lot about the system and also how to debug make errors (^_^)
also check out Arch Linux, its a little advanced, but i love it, once you have the know how you will too. its sort of like Gentoo but with a better community. you basically start off with a core OS that is only a BASH prompt and you download the source and compile everything. you have to configure all the .config files, including your start up scripts. its easer since they use BSD style init though.
you should join a community too. sometimes you run into jagoffs but don't let that discourage you. usually if you mention that you are a n00b looking for guideline you won't get flamed. XD
i also help people out on Ubuntu Forums and Linux Forums