Hi Zach, no problem! Seeeduino 3 will be fine - I think seeeduino are "best of breed" when it comes to arduino. There's two switches on them, one labelled RST (reset) and one labelled VCC (supply voltage to use). Set the RST to AUTO and the VCC to 5v. This tells it to reset automatically when you want to upload a new program, and also to supply 5v to the motorshield. Lots of shields like 3.3v, but the L293D chips in the motorshield need a full 5v. Only thing about it is that it's a "duemilanove" design rather than an "uno" design. This boils down to the way that the USB is handled - the duemilanove uses an FTDI chip for USB interfacing, and that sometimes needs a special driver to install (on PC and mac), whereas the "uno" style boards don't. But it's easy to do.

All the electronics/logic side of things can run off the USB connection, so you can connect, program, even run commands just using USB, and use the servo motor, but the stepper motors themselves won't actually do anything worthwhile unless you've got an external power supply also connected. I've run at about 6v, but I'm tending to use 7.5v lately. Just seems to make things a little more definite and reliable, and I don't see any down-side really - probably runs a little hotter, but I'm getting more fearless. I've got a variable voltage supply because I like to be able to use it for lots of things. (The A4988 or A3967 based stepper drivers like higher supply voltages: 7.5v or 9v.)

Adafruit recommend splitting the power supply, so the motor supply comes into the motorshield through the screw terminal on that board, and the logic supply comes in over the USB (or throught the arduino power socket). You can split them by removing the little jumper that's next to the motorshield power terminals. Personally, I've never had any problems I could attribute to power supply, so I almost always run joined-up, with the jumper in place, and the power supply plugged into the arduino socket. Neater at any rate.

The wire you use for the servo extension doesn't matter much, the one I ship in kits is a neat little thing with a 3-wire ribbon cable with connectors on both ends, but I admit the one I use at home is made of pin-headers and insulated with tape. If you've splicing in-line, offset the splices so they are not all at the same point (so that shorting is harder), and insulate them well. Doesn't need to be thick wire - something that is meant to carry usb-levels of power will be easily good enough. Also, bad things might happen to your servo if you reverse the connections, so be careful with that.

Good luck!
Sandy Noble

No worries Zach, happy to help. The 2A supply will be fine, the motors won't draw anything near that, so should be ok, and like I say, I've been using 6v everywhere up until a couple of weeks ago, so 6.5v will be plenty.

sn