I'm still officially of the opinion that this is relatively unlikely to ever lead to an impeachment, and is very unlikely to lead to a removal from office. However, the path forward is at least visible now, although OP is putting the cart way ahead of the horse. The path is this:
1. Trump did some really bad things that we either don't know about yet or can't prove, but Cohen has proof.
2. Cohen cooperates with Mueller in exchange for government support in seeking sentencing leniency.
3. Mueller finishes his investigation, and sends a report to Rosenstein, who in turn sends a report to Congress.
Simple enough, I guess, but I still contend it's unlikely. The best way to solve the Trump problem is by politically neutering him with a blue wave in November, and then sending him to the dustbin of history with an electoral shellacking in 2020.
Yep, at some point for impeachment to become a serious threat, facts we do not know will have to emerge. They could, Cohen could come up and say he took that trip. That would be the most likely. Even Trump knowing about the Trump Tower meeting isn't likely to be impeachable (though if it happens it should be bad politically but it won't be). Your step 1 is still science fiction to me (and it appears to you as well). But being sci fi is a step up from fantasy.