1) Have been using it for a month, quality is fine; as good as you can expect from VOIP as longs as you have proper QOS to dedicate the required bandwidth.
2) PAP2T seems to be popular choice and is what I am using
3) No documentations provided if you use your own ATA. You should be able to use the basic ATA pre configured settings with few minor changes and by searching the forums here.
4) Call Teksavvy to find out, most likely the change over will happen at end of current billing cycle.
5) Be prepared to be patient with any unexpected issue that might come up but once it is up and running and properly configured, it should be smooth. Make sure you have a good router with proper QOS support or a router that supports 3 rd party firmware with QOS support.