Yes. I feel like you're focusing on the "Oro backstabs us after the assault" case to the point where it unacceptably impairs our actual odds of success. Plus, even just considering not dying to Oro, if Oro was planning to kill us and we then show up with little to contribute he might just kill us right then.OK, seriously, we need to make a plan. Does anyone have a better idea than the above?
I think we should be honest. Orochimaru might backstab us after the assault, and that is something we should consider; but he also might genuinely intend full cooperation in the face of an existential threat. In particular, if we link up with Leaf's S-rankers, Oro will probably not be physically able to backstab us after the assault; your original idea of leaning hard on linking up with Leaf appealed to me for that reason.
RER 2.0s, possibly supplemented by standard RERs if substrate proves limiting, provide at the very least a devastating alpha strike that will wipe the board of any prepared defences, kill anyone less than S-rank in the immediate blast zone, and might kill some S-rankers too if we get lucky. In combination with a max-range Air Leadener activated after the initial barrage, they might let us pick off S-rankers even when they're prepared, all with approximately no risk to us assuming we can set them up without being spotted. Downplaying that to try to get Oro to be more willing to link up with Leaf seems ... foolish, especially since the runes you suggest we focus on instead - defensive runes - do not effectively defend Leaf from attack or siege. (High-level Earth Element users or high-level Physique will bypass Iron Earth under its current mechanics, and we don't know how Force Domes would hold up against Samehada's drain, Amaterasu, or whatever esoteric BS Sasori can bring to bear; not to mention that it doesn't block teleportation.)
To sum up, I think we should present our plan as an RER 2.0 alpha strike followed by Air Leadeners and the subsequent shots of the RER 2.0s to pick off survivors, with Boss/Essie rush as a backup plan for when some of them inevitably aren't killed by that.
I disagree with this point. I remain of the opinion that Kisame's chakra sensing range probably doesn't extend for kilometres, we can dodge Hidan's blood sense using Oro's biosealing procedure or maybe even just using SCs, and Akatuski's other sensory capabilities are limited (Itachi doesn't have the chakra to keep any decently strong crows out 24/7, for example). I also think that teaming up with Leaf is totally compatible with RER 2.0 setup if it turns out we can carry the blanks in from the Seventh Path; if we can't, there is a problem in that we can't make SCs and refill them to shape the blanks without Noburi onsite but we can't get chakra from Leaf without Noburi in Leaf, but Noburi can carry 2000 CP and Oro can carry at least 2000 more; that's enough for quite a few runes even without access to much in the way of refills. Plus, remember that even if we can't carry RER 2.0s from the Seventh Path, it's much more likely that we'll be able to carry standard REs, and those are nearly as effective for demolishing structures and killing non-S-ranker backup.This isn't a big loss, as we really don't have the stealth to hide for Akatsuki senses while setting up, or the chakra to set up, and the setup for RER2 spam isn't very compatible with the better strategies of teaming up with Leaf for Boss/Essie Rush.