That is very good advice. Many people seem to think of a bitcoin address as an account number, used to keep track of all the funds that they have access to. It really should be thought of more like an invoice number, used to keep track of a single payment. Your wallet software can then be thought of as keeping track of all the invoices (both paid and unpaid) and assisting you in keeping track of it all.
but this can cause confusion, if i want to differentiate the income on my wallet, if i want that, for example all my mining earning go to one address all my signature earning go to another, and i don't like to create a new wallet each time
If you use Bitcoin Core or a wallet like that (that saves a wallet.dat file with all the private/public keys) remember that each time you generate a new key, your last backup will not have this key. Since it's recommended to generate a new key for each transaction
Absolute nonsense. Bitcoin core pre-generates 100 addresses and private keys for you so that when you request a new address it can just choose from the pool of already backed up keys. Please, take your signature spam elsewhere.
but what he say it's true, when you exceed the 100 pre-generated addresses