I've never seen real winter. Erasmus student from South Italy needs your best tips for Helsinki weather! 🇮🇹✈️🇫🇮

Hi everyone!
I’ll be moving to Helsinki for an Erasmus exchange from August 22nd until mid-December (at Aalto).
Here is my "problem": I am from Southern Italy. I am absolutely not used to freezing temperatures, and my current wardrobe consists mostly of t-shirts, light hoodies, and jackets that wouldn't survive a gentle autumn breeze in Finland. I know that from late October onwards, the weather is going to get real.
I’m trying to prep in advance so I don't freeze on day one.
I would love to get your local advice on a few things:
**What am I missing?** Besides the jacket, what are the absolute non-negotiables for the Helsinki late-autumn/winter? (Specific types of boots, gloves, socks, etc.)

**Where should I shop?** Since I'm a student on a budget, what are the best online websites or physical shops in Helsinki to buy winter gear? I'm totally open to second-hand shops/flea markets (kirpputori) if you know any good ones for winter clothes.

**Should I buy now or wait?** Is it better to buy things like thermal layers and winter boots in Italy (e.g., Decathlon/Uniqlo) or should I just wait until I land in Finland to get the "proper" local gear?

Any tips, brand recommendations, or survival hacks for a Mediterranean student experiencing the Nordic darkness and cold for the first time are highly appreciated!
Kiitos! 🇫🇮