The dates should be included with all new documents (since we launched the new website), so if you spot one without a date field then it is older than Oct 2012. If I run out of things to do one day, I may go through and fix the old ones
. Also, if you want to receive notifications of document updates, you can subscribe to the "critical bytes" RSS feed on the developer page:
http://www.thisisant.com/developer/
To answer your main questions:
1) You can get the RSSI value on a connected channel - take a look at 7.1.1.2 in the ANT Message Protocol and Usage doc.
2) A slave can only have one channel connected to the same channel ID (device number, device type and transmission type). So it's possible to connect a slave on two channels to the same master device if it was transmitting e.g. Heart rate and Bike Power, but for your purposes it sounds like you don't have to worry about it.