- You don't really need to look to open source - the free limit for Kinetis is something like 128K for the Special Edition (free) so I don't think that will be an issue. Eclipse is open source as is the ARM GCC compiler, but you really want the debugger. It appears that support for Linux has been dropped in 10.3, sorry but Freescale has to make money, and I'll be willing to bet they did not sell any Linux licenses. Note that the Eclipse used has special plugins from freescale.
- The toolchain will work on Linux, however good luck on getting GDB to talk to the BDM (JTAG). On the other hand, on of the big fails of Arduino is debugging on any platform, so perhaps this is not an issue for you.
- The Zigbee Shield does run on 3.3V and it uses the serial port, so there should not be an issue. YHou have to understand that there are two levels of drivers - above the actual serial port code, you need to driver the zigbee module, but this is pretty simple and you could look on the Arduino code for this.
Linux has very little professional level support for MCU's, so I use Windoze for this. But I do it for fame and fortune (and fun) so I must have a source level debugger. Generally, freescale supports Linux when it make commercial sense to, and is a member of Linaro and the Linux foundation.