All good questions, none remotely stupid. As the others have said, the oncologist will answer them all and more you haven't thought of as well. Take notes, or ask if you can record the appointment on your phone. You get a lot of information at that first appointment and you'll think of a lot more questions as a result.
Very quickly it will become second nature, so try not to stress in anticipation. It's a steep learning curve but you'll both do it. Have you and your wife accessed BCNA'S My Journey online tool? That will be a tremendous help for you both if you're hungry for information.
But to answer a couple of your questions, yes, the effects of chemo are cumulative, but not all of them. Generally speaking you'll be more fatigued at the end than at the start.
Exercise is very important and the most effective thing you can do to reduce the side effects. I walked almost every single day during chemo, starting with a short slow stagger up and down the street, and building up to a brisk 5kms by the end of each cycle (except the last, low bp problems and my heart beat too fast. Common on TC).
Your immune system is very low only for a few days in each cycle, the onc will tell you which. Be extra vigilant then with germs, but otherwise general caution should be sufficient. Keep friends and family with germs away, but you can't do that with your own kids, so you just do your best. I had four in school when I had chemo and I didn't get sick once.
I began seeing a dietician when I commenced chemo. She was thoroughly acquainted with cancer treatment. Broadly speaking they don't want you to gain or lose too much weight. She said 5kgs in either direction was OK. The big thing was to keep your nutrition up, and in the face of changed or lost appetite, to increase your protein intake a bit. But all the usual rules apply: lots of veg, two serves of fruit a day, lean protein, complex carbohydrates etc. Food can be a challenge because chemo can make you crave weird stuff and/or totally knock out your tastebuds. By the end of mine I could taste virtually nothing. However six weeks later it was back to normal. So, see how she goes and get your GP or oncologist to refer you to a dietician if you feel you need extra support in that area.
Like @Afraser I want to say that while a reasonable amount of anticipatory research is handy, the breadth of reactions to the same drugs is so wide, that it's better to take things as they come. Some work all the way through, others can barely get off the couch and most of us fall somewhere in between. It's grotty but it's doable. Easy to type and harder to do, but in my experience, cancer is very good at teaching us to focus on the present.
Take care, and hugs to you both. K xox