I think the "mineral rights" deal might play into this. In the full interview[0], Trump mentions it right off the bat, and talks about how it "means we're going to be inside".
I think it goes in tandem with your number (3). Like you say, why would Russia not violate the agreement? I think maybe the move is "well now we have citizens in there working so don't blow us up". It's one thing for Russia to attack the Ukraine, but another if they have collateral damage that takes out Americans.
I don't even know how valuable the actual underlying resources are, so much as a bit of "kayfabe" between the Ukraine, US, and Russia, that things are different.
Anyway, that's my hope.