1. Go meta or go home.
The entire adventure is set up to appear to be about Michael Bay, but it isn't. The giveaway is in the title- it's named after a Coen Brothers movie. That's right- the entire adventure is, in fact, a Coen Brothers movie. The gist of most Coen Brothers movies is that they start with a Simple Plan, but because people are who they are ... it fails spectacularly. Here, we have Michael Bay with his own simple plan- he is going to have a do-over. He is going to re-do his career and get the respect that he thinks he is due, and since he has a time machine, he can do it right by working with true artists, and basing his movie off of Shakespeare, and not repeating his mistakes.
Except he can't. He's Michael Bay. He's going to do the exact same thing he always does. The irony of this adventure is that Bay hasn't enlisted the Coen Brothers to help him create his movie; instead, Bay has set in motion a real-life Coen Brothers movie. People who can't help but be what they are, and spinning that out to horrible consequences.
2. Using the ingredients in multiple ways.
Simple plan- Michael Bay has a simple plan to be a great filmmaker. The film that he is wrecking (Blood Simple) is a canonical "simple plan" film. The Coen Brothers are considered the archetypal filmmakers of the simple plan trope (if you look up the trope on tvtropes, the Coen Brothers have their own section, and it's listed first).
Credit Due/Poor Reception- Both Michael Bay and the Coen are struggling with this. Michael Bay is motivated by the poor reception of his films, and wants credit for the film that he is making as an artistic masterpiece; but the way to persuade him is to convince him that he receives credit for his non-artsy films. The Coen Brothers want the credit for their artistic ambition, and are worried about the poor reception for the film that they are making.
Dogs of War- I had fun with this one! This is the canonical line from Julius Caesar referenced by Nic Cage when the party appears on set, albeit spoken in that peculiar way that Cage might choose to do so; it's also the name of the dogs/Transformers that report back to Bay, and it's the name of the Pink Floyd song (the anachronistic song, since Bay is using a 1987 song in a 1984 movie) that Bay has on the soundtrack to the movie, because Bay has never met a musical cue that was too obvious.
Last Knight- Okay, this was the one I really enjoyed, since it sent me on a whole tangent. In addition to a chess piece (knight), it's also the movie that set this whole thing in motion (The Last Knight) and the character that is the Last Knight in the Last Knight (Marky Mark). Since it's the time machine that is necessary to resolve a major part of the adventure, it's also the most important piece, which loops back to the idea of the chess piece. Word to your mother.
Reality Breach- Yeah, I couldn't do much with this. Save the world. Something something glow-y timequakes.
3. Try to give the players options.
Based on the feedback from Iron Sky, I'm guessing this didn't come through at all. The general idea was that there were three main goals for the players:
A. Get Bay to return to his time.
B. Get the Cohen Brothers to get back to shooting Blood Simple (which would require financing).
C. Get Cage to agree to be released from his contract.
The issue in the adventure was that everything was in tension- a sort of equipoise. Flattery to Bay, if the Coens found out, would make it impossible to convince the Coens to do anything. On the other hand, acknowledging to the Coens that the movie they were making sucked would alienate Bay (and the dogs were always watching). Finally, even if that needle was threaded, there still would be the issue of getting Blood Simple back on track, and that would require financing. And even if that was done, what could be done with Cage?
That's why there were hints of what could be done throughout the adventure; the first thing is that I put in a MacGuffin- as in any "Simple Plan" movie, and Hail Caesar specifically, time spent with Arnold would always be a waste - he couldn't help with anything, and if the party tried to use his "advanced weapons" against the Transformers ... it would end badly. Instead, there were other ways for an enterprising party to solve issues (Uncle Frank is, of course, Francis Ford Coppola; Cage and the Coens could be convinced to cast Cage as Hi ... and so on). In short, there were a multitude of ways to solve any problem scattered throughout.
I even put in a Bay-esque solution. If the players really wanted to take out the Transformers, well, the whole set is rigged with explosives .... just set them off and walk away, slowly .....
Anyway, this was tons of fun to write. Best of luck to everyone!