Since Mrs Romeo is minding her own stuff, I find some time to answer your questions.
1. There is no general restriction for noisy aircraft on German airfields. If your aircraft meets your national regulations then there is no promlem flying in Germany. As stated above, you'll probably be asked to present the a/c's noise certificate. The lack thereof will in most cases result in significantly higher landing fees.
2. "Flat" is in the eye of the beholder. The south of Germany is litterally littered with mountains and rivers, resulting in a change of weather every other 50 NM. The closer you get to the Alps, the more influence effects like foehn have. As long as you are not counting minutes going VFR will not be a problem.
3. The most important rule concerning airfields in Germany is when they're closed they're closed. Many smaller airfields are operating on weekends only, landing there during the week might even result in legal prosecution, sued more often than not by neighbours complaining about noise.
You are not required to file flightplans in Germany or in Austria, as long as you are not crossing the border, eg to and from France or Belgium. There is no need for flightplans crossing from Germany to Austria.
4. I'd strongly suggest tuning onto FIS frequency while en-route. First of all they speak English and can help you negotiating restricted areas. Many of the smaller airfields are run by local flying clubs and are German only, even though English may be understood. If you appreciate help getting in and out of places you might consider planning via airports with class D or class F airspace, however avoiding the larger ones (all with EDDx as designator). It's for example Friedrichshafen (EDNY), Augsburg (EDMA), Mannheim (EDFM), Karlsruhe-Baden (EDSB), Schwäbisch Hall (EDTY) or Zweibrücken (EDRZ), most are Radar equipped and can guide you along. Other airfields you might think about are Freiburg (EDTF), Mosbach-Lohrbach (EDEM), Rothenburg (EDFR), Egelsbach (EDFE) or Landshut (EDML). I can't give you any information on places to stay at or to find something to eat. Most fields will have a restaurant close by and certainly a helpful soul pointing you in the right direction.
5. I won't comment on maps. As stated above, check with your local dealer and see which suit you best.
Final comment: As long as you know your stuff, flying in Germany is very relaxed and easy. Just hit the starter swich and off you go. I hope you enjoy the time.
FR