So I think I may have answered my own question.  I found this Gumstix pack at the store  I suppose I should have bought this package instead.  I want to set up my system so I can flash the verdex-xm4 without disconnecting my robostix or netwifimicroSD.  The tweener product page says the tweener cannot be used with the netwifimicroSD as the ethernet port physically blocks it.   I think my other option is to use the console-vx instead.  Or is there another expansion board that will provide serial/USB connectivity without disconnecting the other boards?  It would be ideal if I could just have a stack of four boards fastened together and mounted in a custom enclosure. 
If there is no expansion board compatible with my existing 3 boards, then I see myself as performing these steps:
1) Connect netwifimicroSD to verdex-xm4
2) Connect consol-vx to verdex-xm4
3) Set up Linux build environment on development PC
4) Connect USB or serial null modem
5) Connect 5V power adapter to either expansion board. Power will be distributed to all boards automatically
6) Configure build to use netwifimicrosd and robostix and compile new image
7) Flash verdex with new image (or is this supposed to be done with power off?)
8) Establish network connection.  I intend on setting up a microSD file system and writing C programs to the system directly using SSH.   
9) Disconnect power, usb/serial cable, and console-vx
10) Connect robostix
11) Connect power to Robostix to reboot system
12) Should now be able to interface through wifi or ethernet using SSH to write software to my Gumstix system.  I will write programs to drive servos, read sensors, etc.
Any advice? Recommendations? 
Also, I'd like to get screws and spacers for my boards.  I don't know the exact size.  Anybody have part number numbers for screws and spacers?

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