1. Fall seeded wheat, barley, triticale and rye are hard to tell from each other at this stage. The order mentionned is the frequency of occurence. It is the common practice to make tramlines. Most seed drills are 3m wide because of road legality. Common spray boom widths are 15, 21 and 27 m in the smaller structures of central/western Germany. So tramlines are drilled every 5th, 7th or 9th pass. Usually there is an electronic controller counting the passes and shutting off metering wheels in the box drill. On air seeders there are magnetic flaps in the seed tubes.No GPS involved. It's the poor man's GPS :-)

2. It's mustard cover crop

3. Those manure tanks with inflated roofs are biogas digesters. There are many due to subsidization. A fixed rate per kWh power produced was guaranteed for 20 years so they were nice to pencil out. Some older ones are 10 and more years old now and need being worked on. Hard to calculate this type of maintenance or improvements now without guarantees.
There are just covered manure tanks (to retent ammonia fumes) also but most of what you have seen were digesters.
Already Mark Twain wondered how tenderly Germans care for their manure piles. How little things change ;-)

4. Yes most corn is cut for silage, either for cows or the digesters. Some is combined for corn cob mix for hog feeding. For grain mostly in the warmer parts of Germany, like the upper Rhine valley. Anyhow, corn stalks ought to be chopped/mulched /"bush hogged" here to prevent corn borer from spreading. It's a new-to-us pest.

5. Hope I could help, glad you like it here!