So I've read the manga till chapter 67 Demon Lord evolution is happening or should I start over to chapter 1? Edit: or
Chapter 1 and you will be able to understand more of the story and well the manga and the wn are a bit different.
First things first. The Manga is adapted from the Light Novel. So if you read the Web Novel you will find inconsistencies from some parts of the story as the author changed some things in the Light Novel. Like adding new characters that was not present in the Web Novel. But if you read the web novel I suggest read at the demon lord transformation arc. If you don’t want to start from the beginning.
The novel version have much more monologue than the manga, you could feels much more closer to the characters and their feelings etc. I've read the webnovel first till the end then i read manga till the latest chapter. All i can say is that in manga you don't feel particularly close to Rimuru's underling, and why he strongly feels to not hurt human, and then his madness for humans who killed his followers. The manga version shows that he's angry, but thats it. He doesn't seems particularly, seriously sad or mad about it. in novel, the interaction, every thought he have, everything is revolved around his followers. If you're lazy sure you can just continue from wherever you left on manga, but that would be akin to skimming through the novel. If you truly want to enjoy the series then i believe reading from the very beginning is the best course of action