Middle node seems best to me as well, then your supporting services like this. This doesn't use any exit nodes at all.
The bandwidth on this is so tiny. Tor can handle this. Unless everyone uses it which i doubt will happen. I didn't include files and images for a reason. That takes a lot of bandwidth away from the network.
Haha, nah. You can only revcieve calls when listening and users will need your address and shared secret to make contact.
Would be a low conversion rate for spammers.