Hi there
1. What symbols are you talking about? , on my i40 with a similar (but European mapping) all the symbols are pretty obvious, a fuel pump for a service station a red cross for a hospital, a fork and knife for a restaurant, yellow arrows on the road indicating a delay, red arrows indicate a blockage, road works sign for road works etc. Do you have different symbols from those?
2. USB random all is not stored when ignition off, you have to select it again, there are many threads on here dating back to 2008 with people bemoaning that "feature". This is not a fault.
3. There is a huge drain on batteries in cars these days, sitting on ACC without the engine running is really a no-no, remember that your unit (even in radio/USB mode) is still operating the maps and bluetooth in the background as well as monitoring the climate in the cabin. Many modern vehicles have this warning and auto switch off, part of the pain of all that technology. Again this is not a fault.
4. Never had a delay when playing through USB, other than at the very beginning whilst the system reads the contents of the drive, is yours delaying DURING USB playback???