Only once have I stayed in a FeWo, for a week. We had kitchen facilities, but there was no breakfast room in the complex, so we had to fix our own breakfast. They did deliver, for an extra charge, fresh rolls to our doorstep in the morning. The first day we went out and stocked up on coffee, milk, juice, butter, cheese, sliced meat, jam. Well, of course, we ran out of a lot of things around the fifth day and had to restock, but we couldn't buy small enough quantities and had to leave a lot behind. Just something to think about.
And, about Privatzimmer (the plural of Zimmer, by the way, is Zimmer - like sheep). Someone on this site once referred to them as "Frau Schmidt's spare room". Nothing could be further from the truth. Usually, they are in a multi-story private home built for a large family but now occupied by fewer people, and they have converted one floor to rooms, each with its own bathroom. In most places there is a common room for breakfast; in one place our hostess greeted us cherrily each morning in our room with coffee and a basket with rolls, etc. Privatzimmer are not common in the core of larger cities since there are not a lot of private homes there, but I find them common in smaller towns. You are not likely to find them on booking websites, as they are usually economical operations without extra money to spend on commisions; use the town website.
I can think of a lot of Privatzimmer in which I've stayed where there has not been a "Zimmer frei/belegt" sign in the front.