I had to use FCP 7 to open and old project. That experience was the equivalent of looking at a dinosaur. That was 2 years ago. How long have you been out of the game
Why not try Resolve (as others have suggested)? Hell, even Premiere is better at this point just simply because it hasn't been dead for 10 years.
Also, it might be better to work with the original codec rather than encoding the files to ProRes. I don't know
whether encoding the BRAW files to Prores before they have been color corrected has any negative effects on the original BRAW files (others can chime in on that), but it sounds like it's time to upgrade that Mac if you want to edit this project properly. So you should honestly assess whether you can work on/edit this project properly with your current set-up. Doesn't look like it imo.
Good luck.