Welcome to TabletPCBuzz!
The link you have is to an LE1600 cable and that is different from the LE1700. We offer the LE1700 ZIF cable here but we're out of stock right now with no ETA from Motion Computing on when new ones will arrive. You might be able to find it elsewhere by searching for the part number.
You can use any pen that is designed for a Windows Tablet PC (Fujitsu, TabletKiosk, Lenovo, etc.). The cheapest that I have found are these Fujitsu pens. The only downside is they won't fit into the LE1700 pen garage. If that is important, then you have to buy a Motion Computing LE-series pen.
Last, to install the OS you will need to call Motion Computing and orders Recover Disks ($30, I believe).
Best of luck with your new tablet!