A Feed/B Feed. If I choose both A and B feeds, is there the potential for contention? How do you arbitrate between the feeds? Is one preferred by the handler over the other?
Udp does not guarantee packets transmitting. So to minimize possible loss the 2 feeds is used. The handler processes the first received packet and skip the duplicated one. The additional actions are to received the duplicated packet and parse sequence number to skip. If there is a good internet connection, the only one feed can be used. Also A/B depends on the network environment.

Logging. Currently, there is no way to turn "off" logging in Xetra MDI. Is there a way to completely avoid any logging whatsover in Xetra MDI? If not, which is the recommended setting for absolutely minimal latency?
Error log level is enough.