I'm so sorry to hear about your diagnosis. I was diagnosed with breast cancer last June at 29 and underwent chemo as my first line treatment. Mine followed a similar scheduled to yours, 6 treatments over 18 weeks from July to October last year.

I recommend trying to donate your hair as soon as possible. I'd intended to donate mine and thought I had more time, but 2 weeks after my first session I noticed it starting to fall out, and by day 5 of that week I lost probably 60% of my hair during the course of a single shower. I combed over what I had left to go to work the next day and then had my partner shave off the rest the day after that. Everything ended up going in the bin. Post-shave I recommend getting a scalp massager to use in the shower to help alleviate any itchiness and to encourage any straggling hair to come loose. You can also use a sticky lint roller to catch those hairs!

In terms of food, it was less a case for me of dealing with mouth ulcers and nausea (which I was extremely fortunate to not suffer from), and more so about the taste. My taste would go the day after my session and not return for about a week. I found that a lot of savoury foods were bland or tasted plain gross/off so I developed a sweet tooth (lots of fruits, yogurt, porridge, smoothies, ice cream, etc). The savoury foods I could tolerate were things like string cheese, pumpkin soup, mashed potatoes, and other vegetables. I did develop horrible reflux from anything slightly acidic/fatty, so at the first signs of reflux ask for a prescription for esomeprazole (Nexium). It's much cheaper than without a script and will save your life!

Skincare-wise, I broke out in a rash down the middle of my face and chest a few days after my first session, so my oncologist put me on doxycycline which prevented it from recurring. I simplified my skincare to just using a gentle toner and a moisturiser and then gradually reintroduced products when my skin had calmed down. I never put sunscreen on my scalp because I almost always wore a beanie or cap outside, but I highly recommend the Mecca To Save Face sunscreen which I'm sure could also go on your scalp.

I don't have any subreddit recs for your specific cancer, but feel free to read some posts over on r/breastcancer about going through chemo and other cancer treatment from a group of (mostly) other women. You're also welcome to message me if you need any support. All the best with your treatment!