Conspiracy overly complicated

The conspiracy was overly complicated, and had too many variables for it to have come to fruition. How long did "Angus" have to stay at the lighthouse hoping Rachel would show up? What if someone else who knew the lighthouse was to be empty came out and found him there? What if Rachel did not fall for him? Would it not have been easier just to type a fake suicide note saying she was going to join her dead son instead of Angus? Seriously, type the EXACT same note, only substitute "Thomas" for "Angus", then kill her. Do that the day she got there and it would have been a WAY better plan.

I'm aware that it's just a movie. There's no need to remind me.