3. Bitcoins have to be stored in a digital wallet, either online through an exchange like Coinbase, or offline on a hard drive using specialised software.
OP, this is not correct.
Bitcoin is simply stored in the blockchain, so it is stored on the network, not on a hard drive using specialized software or on an exchange. Only the bitcoin network (thousands of computers called nodes, decentralized around the world) stores bitcoin, no specific computer or exchange or device or whatever stores it.
The way you can ACCESS and transact with your bitcoin is through software called a wallet, specifically using your cryptographic keys. This wallet software could be various different things, including a company providing the service like an exchange, or a specialized hardware gadget, or software on your computer, but that is NOT how bitcoin is stored.
And storing of the actual cryptographic keys which allow you to access your bitcoin through wallet software (whichever kind you're using) is a different thing entirely and that could be stored through a service like an exchange, on a hardware wallet, on your computer, on a usb stick, on paper, in your head, on metal, on anything cuz it's literally just a string of characters so anything that you can write in/on (including 'writing' into your memory) can store your keys.
