I had the genomic testing. Mine was Endopredict and it cost $3000. It will probably depend on the final 'grade' of your cancer once all the pathology is in. It is only recommended for grade 1-2, HER-negative, 0-3 lymph nodes involved and a Ki67 under 10. So it could be it's not grade 3 as first thought or your Ki67 may be very low.
As I chose a mastectomy rather than a lumpectomy (breast conserving surgery), I did not need radiotherapy. My endopredict came back low. So also wasn't recommended for chemo. From memory, scientific evidence supports starting chemo within 3 months of surgery.
It's fantastic that your nodes are clear! It will take a while for that area to stop being sore. I have the mesh holding my implant in place stitched to that area as well and, after 6 months, it's still sensitive to touch.
I can't remember if I was on antibiotics. If so, it was just for the first few days after surgery. The warmth definitely sound like something something your GP to look at sooner rather than later, as it's a high chance it's being caused by infection. I had pains, twinges (especially after a few weeks when nerves started reconnecting), tenderness and phantom pains in my non-existent nipple. But never warmth.
I'm on tamoxifen as I'm pre-menopausal. I don't find the side effects too bad. I take it in the morning as I feel agitated for the first 6 hours (so caused insomnia at night). Vitamin B12 is helping that. And I'm taking magnesium for leg cramps/aches from it. I have inflammatory arthritis/spondylitis, so I can't say if it's giving me bone/joint aches as I already had them! After almost 6 months I'm noticing some issues like UTI-type symptoms that would be caused by it. On the plus side, it has stopped my perimenopause hot flashes and made my skin produce oil again like when I was younger. It doesn't stop estrogen, it blocks the receptors. What they've found is is had an anti-esteogenic effect on some parts of the body and an estrogen-like impact on others, such as the uterus. It can increase menstrual bleeding, but I've had an ablation in 2020 so it's not an issue for me.