1. Click on the Disc tab in the Project panel. Then in the Properties panel you can set the default audio and subtitle options.
2. You're probably just going to want to make your still image longer so the blip doesn't happen so often. Also, be aware that some DVD players may not do this as noticeably. It's very noticeable during Encore's preview, but that's only a simulation and real players (newer ones, anyway) are usually better behaved.