Can someone explain the following:
1) Why are they making such disclosures? Wouldn't they make it easier for hackers to get to them? For example, just for the sake of argument (know it's a bad argument because of math, large numbers, publicly visible to begin with but just put that aside) - if you provide the address hackers can begin trying to brute force it. But if you don't disclose it, a hacker would not even know where to start. It's like a robbery victim pointing hackers where to attack next.
Think the question here is: why are they comfortable with hackers knowing such information.
No. If anything, this actually helps Binance and the community track the activities made on the address. One can always know the public key, as it is what's actually needed anyway for someone to receive funds, without compromising the security of the said address. They can brute-force it all they like, but then again no such methods of brute-forcing is invented to crack open bitcoin.
2) Why do they appear to use only ONE address for BNB cold wallet? Isn't this like putting all your eggs in one basket?
It's a cold wallet. It's supposed to be the storage of pretty much everything, or at least a majority of the resources they control. If they have multiple cold wallets, that means they would employ multiple security measures, and focusing your attention to a single wallet is better than dividing your attention, resources, time and effort in guarding funds. Hackers would have a higher chance into cracking into multiple wallets, too, rather than a single, heavily-guarded one.
3) Likewise, how many hot wallets addresses do they use? Any way to find out such information?
Not sure whether exchanges fully disclose that information to the public.