F454 is about following the systems lifecycle, however you will need a project which enables you to meet each of the bands in the mark scheme. This should be complex enough to meet those bands, i.e. having a real end user for the investigation, use of looping constructs or file writing etc in the code itself. The system should also be simple enough that you do not have to do more than you have to, so getting the balance between simple and complex is important.
Here is an
exemplar project from OCR themselves, the moderators show where they have awarded marks and what they want to see.
I did my F454 project before December last year, and my teacher predicts 77/80. My project was a system to test GCSE student's knowledge of binary, hex and octal conversions, with practice tests and writing their scores to a file in CSV format. There was also an admin facility to read files from within the program with username and password logins.
Hope this helps