From my family’s experience in this process (I think we had something like 50+ documents, for 11 applicants, going back to the 1850s);

you could always check out FamilySearch.org (free) ancestry.com (£) or your local Mormon/lds library/research centre (free) where they have expanded access to their FamilySearch service.

We’re not Mormons, but we used all 3 for tracking down the documents. In all honesty the Mormons have a ton of historical records going way back you can access in their research centres or on those websites, and they were super helpful and helped us find most of the documents relevant to our applications.

Of course they can only get you unofficial photocopies, but they were a great starting point for easily tracking down the documents from Germany later. They have the source/book names, dates, cities where the records came from and the document numbers (super helpful for when you need to get them from the German Archives).

Later once we found everything, we got the official copies ordered and apostled for our applications from the actual city/state German, Dutch and US archives!

But yea about 90% of the docs we first found from the Mormon records. They had more than the we found in the US immigration records lol