I just want to know how those people behind bitcoin secure the money they will invest because as far as I know there are lots of hackers all over the world.
To secure your bitcoin investment you have to put it in a hardwallet or offline wallet that you own the private keys never give your keys to anyone else you do not trust. That's the only and safest way to put your money in a secure place, exchange site is never secure so if you have some their make sure that its only for trading.
your suggestions are quite good enough but i think that is only necessesary if you have a lot of bitcoin on your wallet let say you have over 1btc then that is the perfect time that you must buy a hardware wallet because hardware wallets or offline wallet are also verry expensive nowadays.
it is not really worth it to buy a hardware wallet if you are not earning or holding a good amount of btc in your wallet but instead you may rather stick on the classic traditional wallets . you can then enable 2fa authentication and other extra security measurers to make your account more safer .