No, you don't NEED to use a guide to "play" the game, but without it you WILL get stuck, you WILL miss key choices, you MAY potentially lock yourself out of a romance and waste your time playing through multiple chapters before you realise your mistake. The mission log is very generic - forgot the exact details? Oh, well best get to clicking around. Got stuck? Ah well, best go to the discord and wait for someone to respond.
I think it's disengenous to new players to give them the wrong idea going into this game. It can be confusing and complex. For a renpy novel made by such a small team, its brilliant - but If you want to make your life easier, just buy the guide - otherwise expect intense frustration
I also think you touched on something very important here: "Will you make mistakes? yes. Not every run is perfect" One of the main issues with this game is the amount of time it takes to play through it for one romance. Mess something up? Well that's another 30 hours bucko. Better to try and get everything right the first time so you don't have to redo hours and hours worth of content.