Two thoughts came to mind:

1) A documentary about a trip to the moon and to mars, from start to finish. This means the beginning steps of planning out what is needed, then the steps of planning it all out, buying the materials for travel, the safety procedure, the training, the risks, the family drama, the politics of it...and then document the space shuttle, the launch, the entire trip up (potentially launch two or three space shuttles, and have a camera filming my shuttle from the outside, one from the inside, and also have those carrying the massive amounts of supplies needed), have cameras livestreaming as the fuel thrusters break off and fall back to Earth, have both space shuttles go to the ISS and have a full tour of it, full view of the entire Earth, the Sun, and the Moon from space (and all the surroundings). Then the planning to go to the moon, the actual trip there, having others starting on the trip to Mars with the supplies. The trip to the moon, we go, we land, we walk around, film everything including the flag (shut up, conspiracy theorists), the Earth, the starbucks that's inevitably up there...all of it. Then we go back to the ISS, stock up, prepare, and take the long trek to Mars. Document the difficulties of space travel, the family drama (if the astronauts and their families are ok with it). Back on earth we'll likely see lots of politics and discussion of territory and colonizing space and all that. And finally when we get to mars we walk around and we shake hands with the martians and then rinse wash and repeat for the trip back.

It might take 40-50 years total to create it, but it's an unlimited budget so I wouldn't mind devoting my livelihood to it if it included a major salary for all people involved including caring for their families for life.

2) the exact same thing as above, but a joint movie with James Cameron about the deep, deep sea. I mean deep shit. Building all the stuff we need, the science behind it, and trying to go as deep as possible.

3) Oh, a bonus: a movie about money in politics, where we start a massive, massive, massive investment firm with our unlimited budget and make billions of dollars and we watch the progression of politicians and shady figures trying to come see us. We wouldn't tell them we were making a movie (think Borat and Bruno, except it's about people who literally can order an entire National Security Apparatus to assassinate you). A guy can dream.