How to copy video files from OS X to iPad over Wi-Fi?
AirSharing is a swiss army knife of turning any iOS device into a wireless file server. There are many others, but this program has three versions that have stood the test of time.

The "copy when connected" nut will be harder to crack. Unless someone steps up with a ready made solution, you will have to set up SMNP monitoring of your router and trigger a sync when the iPad MAC address is logged as joining the network. You could also poll bonjour locally, but SNMP seems more elegant to me since it will log and push that join without constant monitoring on the mac end.