1) Do they let your trade without KYC? What's the requirement like for their .com? I heard you can trade €5,000 worth of BTC a day without the need to KYC? Is this still the case?
You have to do KYC if you trade with Binance P2P (peer-to-peer) or OTC trading but I don't see any rule on KYC with trading limit.
They will give you a pop up message for Trading requirements, in which you see "Complete KYC Verification"
P2P Binance's' rule
Identity Verification
Before you can start trading on Binance P2P, you need to complete identity verification, also known as KYC (Know Your Customer). KYC assures that users trade with their authentic identities, and Binance reserves the right to investigate.
OTC trading rule
To trade OTC, your Binance account needs to be verified.
With non P2P trades, you don't have trading limits per day.
Binance does not require you to do KYC but if you don't, your daily withdrawal limit is 2 BTC. If you withdraw more than 2 BTC per day, they will require you to do KYC.
Read:
If you have not completed the identity verification for your account, your withdrawal limit is set to 2 BTC for every 24 hours.
2) If so, then is it something that they say but later freeze your account with KYC demands even though you kept it under 5k and you didn't break their rules? I mean, sure it "could" happen, but is it common with them?
They have rules to suspend or cancel your account
[1] but it is different than KYC requirement for > 2BTC withdrawal per day. If you don't do KYC, you can wait for next day to continue your withdrawal.
[1]
https://www.binance.com/en/terms1. Suspension of Binance Accounts
2. Cancellation of Binance Accounts
3) What are the requirements to do so - name, phone number, email only?
When you register your account, you can use your email or your phone number.
4) Can you trade as soon as you sign up (no KYC level)? How long is the signing up process? Does it require approval? Can you sell directly to them?
Create your account is easy, and fast and you can go to trade very quickly after you finish your registration.
Binance don't buy any crypto from users (but I could be wrong).
5) Do they need KYC to withdraw?
Depends, see above.
6) Is it safe to get referral codes from strangers and use it to sign up?
I don't see any risk. If you use a referral code from someone else, that person (that account) will receive passive income from your finished trade. That's all.