This guide is not about creating paper wallets. It merely describes one of the several ways how you can generate your own randomness and convert it to meaningful words from BIP39 without relying on any hardware or software tools that do the same job but better and faster. If you're not experienced enough and don't understand precisely how the generation algorithm works and why it works this way, it is not recommended to do things manually because there is a high probability of you losing all your money due to stupid mistakes. Even worse, if you decide to generate addresses manually from your manually generated seed phrase, the chances of you messing things up are almost hundred percent because doing sha-256 or ripemd160 calculations requires hundreds of hours of intense and incredibly complex math manipulations, which is infeasible for a normal person. I'd say just buy a reputable hardware wallet like Trezor, and don't complicate your life by reinventing the wheels.