Yeah, I don't think Kuma himself knows any of the important parts of his story that we still need. We know he has no idea what makes the buccaneer people special so that story has to come from someone else. I think he can stick around to see the end of slavery and remeeting up with the revolutionary army but he can get that done by just sitting there and waiting for everyone around him to do it (Dragon will come to him and end slavery possibly, Kuma just needs to remain alive for it).
The reasoning for Straw Hats destinations during the time-skip is a really minor point and doesn't need addressing. We don't know how much Kuma knew about the Straw Hats and their abilities so as far as we know it was random where he sent them. Maybe he saw Nami's weather powers and Zoro's swords and so got an idea of where to send them. He knew Franky was a cyborg and chopper was a doctor, so had idea on where to send them as well. But in hindsight, it's weird to send Robin to the bridge when he could've sent her to Dragon directly. Or even to Iva's island, but instead he sends Sanji there for some reason. You can argue that because Brook was the newest member and no one knew he was even on the crew, that Kuma just sent him somewhere random. The simple answer for Luffy is also that Kuma needed to send him to somewhere he knew Haki was really common and Amazon Lily seems to be one of, if not the only place, where it is actively taught. All the warriors in Amazon Lily know Haki, it would be a great place for Luffy to learn.