How can I set the R830 to automatically default to a wired Ethernet connection when I dock?
If the port replicator is connected to the LAN then the notebook would use the LAN connection automatically if you connect the R830.
How can I disable the wireless connection when I'm docked and using an external keyboard (the F8 toggle to turn wireless on/off on the laptop keyboard doesn't work on external keyboards)
Well, in such case you can use the internal keyboard to switch off the Wlan using Fn + F8