What you are feeling is perfectly normal. My biopsy was done just prior Xmas and a funeral....so I was in such a state trying to fake my way through not knowing my treatment plan. Soon enough you'll have your first plan.
I too was planning a big holiday when cancer struck. 3 years on we just got to have that holiday and it was wonderful.
Breast cancer has many different types and until your pathology is known there is no way to know what treatment is needed. There are many different plans. Some have lumpectomies, radiotherapy and a pill...and that's all that is needed.
I want you to know Australia has some of the best statistics in the world for survivorship. We now sit at 90% survival at 5 years....and with some cancer types it sits at almost 100%
https://www.bcna.org.au/understanding-breast-cancer/types-of-breast-cancer/It does help to read and understand a little before your appointment so that some things are familiar to you. Make sure someone is with you at the appointment who can write things down as it is overwhelming. i don't recommend googling too much (although we all do it I suspect) as it can overwhelm you, especially words like poorer prognosis....which just means it's a bit more challenging to treat...it doesn't mean it isn't able to be treated.
Rally close friends. Get out of the house and do something nice if you can to distract.
@SoldierCrab might have some great ideas.