Marco, the answer to most of your questions (and you know this) is "it depends." To be a little more specific, a "mushroom-like" tumor is a papillary tumor. These can be either low grade or high grade and this requires pathological examination of the tumor to determine. High grade tumors have cells with a very abnormal-looking appearance and a large number of which are dividing. Low grade tumors have cells that are more "normal" in appearance and only small numbers of weird and dividing cells. The size of the tumor is probably more likely to be related to when it was discovered rather than grade. Don't think patient's age has much to do with it nor does the presence of obvious symptoms, which sometimes are due to the location of the tumor in the bladder.
CIS (carcinoma in situ) is another manifestation of malignant transitional cells from the bladder lining. It shows up as a sort of rash on the bladder surface, and because it is not tumor-like it is sometimes missed on an initial TURB (one reason a second TURB is often done.) It can present alone or along with the papillary form. CIS is always high grade.
You really WON'T know what you are facing until you have the TURB and get the path report back. THEN you can face whatever it is with some knowledge.
I know that the waiting is difficult, but try not to worry about all the what-ifs and the odds and the possibilities. Most of them do not apply to you!!!
Sara Anne