I think one of the things I would have liked to have had at the beginning was a feeling of more control. You get swept along so fast that sometimes you think you have no choice, you just have to go with what is recommended. It's all so scary, your overwhelmed with information and fear.
Let people know not to be hesitant about asking as many questions as they possibly can. Encourage them to realise they can speak up if they are not sure and see if there are other options. This is something that needs to be known at the begining instead of thinking you just have to do what you are told because that's the normal way and that's what's easiest for the doctors.
Some people have no idea that breast care nurses even exist so that would be a good topic for sure.
Definitely clear information on costs etc re public/private and does the hospital run a patient travel scheme for remote travel? The last thing you want to have to worry about at this stage is money.
Maybe a bit of a time line as to how things normally work in regards to scans, time delays for results, what's a hookwire, what's a core biopsy etc so you don't just show up to these things thinking you have to drive back to hospital with a coathanger sticking out of you boob :)
Maybe a mention about the cold cap.
How to get through that morning before surgery when you look in the mirror and realize that this is the last time in your life you are ever going to look like that.
If you can get through on how to handle some of these emotions and that they are all normal you will have done a better job than just the technicalities.