For tracking projects in portfolios, you can use either Status, Custom Fields, or both, as you find helpful. You can implement metrics in any, albeit not precisely like Asana implements Goals metrics. Milestones, too, can be markers to tick off along the way.
Regarding the duplication question, I think that might stem from a misuse of Goals. If you read about OKR or other Goal frameworks, I don’t think they intend to correspond 1:1 with projects.
Goals are outcomes with measures–SMART or better yet, SMARTIE measures.
Projects are work which you can track as mentioned above.
Although projects carry out goals and Asana allows you to associate projects to goals for this reason, making a project a sub-goal of a larger goal is not their recommendation, I don’t think, and leads to your duplication issue.
I hope that might help, though perhaps you’ve considered all this already and ruled it out, in which case, ignore!
Thanks,
Larry