Having been a game developer for several years now, I've had the opportunity to specialize in projects particularly revolving around multiplayer servers, with my expertise being most pronounced with GTA 5. Over the years, I have gained extensive knowledge in shifting and modifying the gameplay mechanics of GTA 5 to fit various server setups - a skillset that will prove invaluable for the perfect implementation of your envisioned role-play experience.
Moreover, I have successfully integrated novel missions into existing gameplays to engender engagement and longevity. Your project's requirement for "In-Game Economy System" is also something I'm well-versed with: I understand its significance in adding strategic depth to the overall gaming experience.
Another area where I stand out is character customization, as well as interactive NPCs, combining these features culminate into an immersive world teeming with personalized storylines.
In conclusion, a project of this caliber not only requires profound cognizance of GTA 5’s fundamental principles but an intuitive comprehension and ability to adapts those concepts towards constructing an exciting role-playing environment. With my abilities and experience, our collaboration promises to actualize something not just amazing but awe-inspiring. Let’s embark on this gripping journey together!