Logic's demo is a decent starting point (you have to register a Zoom kit for access).
For cross toolchain, many people are using Code Sourcery Lite:
http://www.codesourcery.com/sgpp/lite/arm/portal/subscription?@template=lite
You can use the above toolchain to build the kernel. For kernel, start with the mainline from kernel.org then apply the Logic patch set.
For RFS, you can boot from Logic's elf, tar up the RFS files, and copy the archive to an SD card. Untar on your Linux desktop, then customize (edit startup scripts, rebuild busybox, etc.). Then you can build the file system image to load back on the target. Will post some additional notes on this later.
I eventually went with the TimeSys solution. Their "factory" build system saves a lot of time otherwise spent on book-keeping, and the build is fully automated. (I used labor-intensive manual build instructions prior to TimeSys).
~CN