Hij Kate, sorry you've joined our club and especially at such a young age and with very small children.
I got 2 girls too (4yr & 1yr) but I wasn't breastfeeding the youngest when I was diagnosed as stage 2, grade 3 (aggressive). I've had lumpectomy and full nodes removal and am now going through chemo.
All I say is that make most of whatever time you have before your treatment begins so def go for the holiday. I even managed to get abroad to see family over Easter in between my chemos but it will be so much easier for you to do it before you go through any treatment.
FYI, the nodes removal meant that I couldn't drive for 3 weeks nor carry/put to bed/take to nursery the youngest as my arm and shoulder were not working. Be prepared to get help with the kids and also ask for a physio referral to get mobility back to your arm and shoulder soonest.
Be also prepared for emotional rollercoaster and believe me the worst part is waiting for your results and treatment plan but it does get better down the line and you will feel more in control again. x