So sorry to read what you have been going through. I wouldn't worry about a stent spreading cancer, but I am sure you would rather not have one.
There is a LOT on this forum about BCG. There is quite a thread, for example, as the first listing under the topic "Non-invasive Bladder Cancer" here.
It is GOOD that the urologist is going to do an extensive TURB. You don't want him to miss ANYTHING. Many urologists do a first TURB and then, about three-six weeks later, a second. The first time they take samples for biopsy, of course, but by the second they have an even better idea of where problem areas might be and do a more thorough job. My first TURB showed papillary (low grade) and some areas of "irritation." When we went back a few weeks later, and the urologist paid special attention to the irritated areas, they turned out to be high grade CIS. I am grateful that these were found, as the outcome might have been quite different if they had not been.
As you will have read, BCG is NOT chemo where your entire body is exposed to the agent, but rather immunotherapy which is localized to the bladder. However, the bladder IS part of the body
so over time you will probably have some systemic effects. I was very uncomfortable the afternoon of the installations (some people do go back to work...I couldn't have) and then, particularly the following day or so, there was fatigue. But I was able to go on about my usual life, and most people are. As the number of treatments you have add up, you will probably have more noticeable side effects, but it is very do-able. AND those side effects are telling you that your body IS reacting to the BCG with an immune response, which is exactly what you want to happen.
Do hope that you have finally found a urologist in whom you have confidence and whom you can talk to!!
Sara Anne