Hi Braumeise,
You've got lots of good info here, so I'll just add a few thoughts:
I would applaud your determination to make things from scratch at every stage, and recognize a German desire to do things the "authentic" way (my wife is German - we debate this often). I wouldn't necessarily say that you must use a kit, but extract (and some hop pellets, and an appropriate liquid yeast) rather than grain would be a good choice, as would starting with a hefeweizen if that's a style you also enjoy.
It seems that most people starting out on brewing focus a lot on recipe and ingredients, whereas I would suggest that more experienced brewers tend to place a lot more emphasis on the process itself as being the heart of brewing. There's not a huge difference between the recipes used in many different beers (especially in the wheat or pale lager families), but subtle procedural points make big differences. There are award-winning beers made with extracts, and poor beers made with all grain, fresh hops, etc., etc. The process is actually probably more than 80% of good brewing.
I would suggest that you focus on getting prepared to have a strong/healthy fermentation (IE - well-oxygenated, good temperature control, appropriate amount of healthy yeast), and get comfortable dealing with the time, space, and weight challenges involved in a brewday. It's a different animal than bread - bread isn't heavy, isn't hard to cool, or to move, and is generally made with flour you bought already milled and ready to use. If that's not a "cheat" in baking, then extract isn't a "cheat" in brewing.
At the beginning, you don't want to have 30-40 possible reasons why you didn't get the result you were hoping for - 5-10 would be lots! If you use all grain, then water chemistry isn't a big deal, unless you live in an area with water that is an issue, or choose to do BIAB, in which case tannins can be more of an issue, especially in a lighter beer. Respectfully, if your experience is at all like mine, you probably won't initially know precisely how to describe unintended flavours and results, and will have to rely on trial and error to isolate causes. This same dynamic is true at a number of levels - there are many questions to answer, and starting with only a few things mean that you have a fighting chance of knowing where to start solving problems if you aren't totally happy with the results. (Extract basically means you can cut out a few major possible areas of difficulty, and yeast provides an awful lot of the flavour in hefeweizens, anyway, so it's not a big compromise.)
Finally - reading and reading, and reading is a great start, but there's some element of actually physically coordinating brewing in your space and with your equipment that books won't necessarily prepare you for, but that can be a big factor when you've been brewing for four or five hours, and have 23L of hot liquid that then has to be cooled, transfered, oxygenated, moved into a fermenting space, and inoculated with yeast without doing anything wrong. Mistakes at the beginning of the process are actually probably less critical than mistakes at the end, and mental fatigue can be a factor (even if no one wants to admit it). Picking something less complicated to make lets you focus on the essential first steps. If you had never driven a car, and read everything on the internet about how to drive, you would probably be ready to practice driving around an empty parking lot. You wouldn't be ready for the autobahn, though. The way you use the car may be the same, but one is too complicated to reliably do right the first time.
In any event - happy brewing, and good luck!
