You are doing all the right things and your concerns are natural and pretty much what we all go through. When I had a worry, I always did what I could to reduce that worry. Sometimes this was reading about the issue (in the info from the doctors and BCNA) and sometimes by taking some action.
To reduce the worry of catching a bug or virus there are some things you can do. Practice good personal hygiene ( I had a shower morning and night, always washed my hands before eating, had a special glass that only I drank out of, had a particular chair in our living area that only I sat on) Have visitors wash their hands when they come, we bought a bottle of hand sanitizer that was kept at the door! Have a small bottle of hand sanitizer in your handbag and use it after touching things like trolley handles or door handles. Avoid going out if you can in the week that your immune system is most affected (usually the 2nd week if you are having chemo every 3 weeks). Knowing you are taking precautions can help to make you less worried. Also ask people not to visit if they are unwell.
Exercise will help your mind and body. It helps strengthen your immune system and reduces stress. Yoga would be excellent, walking is what I did.
Biotene mouth wash and toothpaste are great for looking after your mouth care. I also changed my toothbrush (a very soft one) each round of chemo.
The first chemo is hard because you don't know exactly what to expect. But in my experience the chemo nurses were very reassuring and take special care of you for that first round.
In my experience I felt unwell (a bit like the flu) for about a week after chemo, then started to feel ok but you have to be careful of your immune system for the next week and then felt pretty normal and well for the third week.
Wishing you all the best and I am sure that you will get lots of helpful advice on here. Take care. Deanne xxx