1. Is there a limit to the bandwidth available over the data channel

There are a no (hard coded) limits to the data channel. However, the user can be limited by the network capacity as well as its own pc/laptop capacity to encode transmitted data. 

2. What type of data can be sent over the data channel?

Currently, the data channel works best when sending strings, but can also sent selected binary types. 

For more information, please view the plugin's compatibility matrix: http://confluence.temasys.com.sg/display/TWPP