Right now, I imagine Trump would be very quick to point the finger at Iran if any kind of action against US assets or interests occurred. Iran absolutely cannot afford a direct conflict with the US, and the real threat may be that a faction sympathetic to Iran takes action that the regime hasn't sanctioned, and Trump uses that as a premise for an attack (I don't see him waiting on the outcome of any prolonged investigation).
Iran will want the whole situation to go very quiet while it uses its influence in Iraq to push for the expulsion of US forces.
No doubt about it. It will probably come by way of Hezbollah in some random country or by Quds Force operatives in the region.