Once single cells came along (and how did that happen is THE big unanswered biological question), the next big step was the evolution of nucleated cells–eukaryotes. This took well over a billion years and–who knows–might never have happened. That is, IMHO, the biggest unknown in the Drake equation. It apparently happened what a big cell ate a smaller one and the smaller one managed to avoid digestion and take up residence, and also reproduce when the big cell did. Then somehow the small one evolved to hold the genetic material of the big one. Somehow. From that point, multicellularity evolved and the rest is details.
As for intelligence, the dinosaurs were around for, IIRC, 165 million years, were at least somewhat bipedal with arms that could have become tool using and never developed anything like human intelligence.
If any species tries to follow us, they will find an earth sadly depleted in natural resources.