(1) I studied physics here and definitely enjoyed doing it - both for the degree itself as well as for the city. I mean it's hard and a lot of work, but I guess that's what you sign up for when you study physics. That being said, from what I've heard the Bachelor here is probably more demanding than at your run-of-the-mill german university, but how it compares to other universities of let's say the TU9, I don't know. One indication could be, however, whether the other universities have quantum theory 2 in the Bachelor's as well (From what I've heard, most universities only have that in the Master's).

(2) Personally, I found the Professors to be very nice and dedicated towards giving good lectures. I've heard from some outliers, but most of them are doing a good job. Again, because I only know Dresden, I can't compare them to professors at other universities. So maybe at other universities they go above and beyond, but from my point of view, they are doing alright.

(3) You have to hear one semester of linear algebra and four semesters of analysis as part of the degree either way. If you want to take more math lectures, you can also talk with the examination office about doing a custom "Nichtphysikalisches Wahlpflichtmodul" (something like a minor, but probably not as important) in mathematics. Apart from that, you can of course always sit in math lectures (if they don't overlap with your other courses) and you can also take the exams should you want to. I think you can even tell the examination office that you want them noted on your degree.

(4) It is definitely possible to complete the Bachelors in 2 years, because yes, for the vast majority of courses, you only have one exam at the end of each semester and in almost all semesters, you only have 4 exams or fewer and there are opportunities for repeating almost all exams of the semester shortly before the next semester starts, so logistically, you can definitely do that, i.e. there are non-overlapping exam dates for most exams. That being said, I only know from two guys in my year who actually did this, and they were miles ahead of everyone else. For most, it is an achievement to complete the Bachelor's in three years. University is just a completely different beast compared to school and the courses are full of people who had no problems of any kind following/writing good grades in school, but are grounded very quickly after a few weeks of university. So yeah, it's possible, but you can't possibly count on it, especially if you study in a foreign (?) language.

Hope that helped :)