Should we start making dough with water or with flour?

The best thing is to do as your recipe directs it, because there are several considerations that play together here.

First, if you have a very exact recipe where you measure each ingredient and mix together in a mixer, it doesn't matter that much. Just dump it in the mixer and turn on, making sure to scrape or rest as needed until the texture is right.

If you again have an exact recipe but are mixing by hand, I suggest that you do it flour-first, because that reduces lumps.

If you have a recipe where you are starting with one ingredient and are going to add more of the other until the desired consistency is reached, the main constraint is the yeast. If you are starting with the yeast in the flour (as is typical with dry yeast), then you should always start with the measured flour+yeast mixture and add water until ready. If your recipe has you start with the yeast in the water (needed for cake yeast, but some converted recipes also suggest it for dry types of yeast) then you should be adding flour to the water and not the other way round. Here, you can avoid the lumps problem by not dumping flour on top of the water, but using the volcano method where you add the water to a depression in a flour heap and slowly mix in more flour from the crater walls until you have it the way you want it. The volcano method works better on flat surfaces rather than bowls, you can use a baking sheet or a big baking tin to gain some control of the mess.

In bread making, I doubt it matters much. Your initial step is to get the flour hydrated and begin the development of the gluten structure. You are going to be mixing and kneading (or stretching and folding), so dough will smooth out significantly after the initial mix anyway.

I'm reading some German homebaking blogs. The message there is usually to keep a bit of water back and add it gradually if needed.

Reason for this is that the flour-to-leavening-agent-ratio shall be kept constant, therefore no flour should be added.

I don't think it matters which ingredient you add first, assuming you are mixing them thoroughly.

More important for bread making is how long the flour and water mixture sits before you proceed with the recipe. This is called "autolyse" and you add together only the flour and water (no salt, yeast, or other ingredients) and just let it rest. This hydrates the flour and begins the gluten development. Most recipes call for 30-60 minutes, I have read studies and experiments that say that longer than 60 minutes does not make a difference but that first 30-60 minutes does definitely make a difference in the texture and flavor of the resulting bread.

In case of dough that is kneaded for a longer time, it is better to add all the flour right from the beginning and rather add more water later if needed.

The reason is that through the kneading the gluten structure is developed and when you add flour later in that process, the later-added part of the flour will be in a different state of this development which might lead to non-optimal results.

It is certainly easier to get a viable dough when one adds the flour to the water...Keep stirring and when the dough get manageable stop adding water. I find it much quicker and easier.