Web Platform Progression and Economy System Design

I’m building a new web-based product that relies on a compelling, retention-driven progression loop rather than traditional gameplay. I already have the feature ideas in place; what I need from you is the math and structural design that will keep users climbing, comparing, and coming back... (Budget: $250 - $750 USD, Jobs: Data Analysis, Documentation, Game Design, Game Development, Level Design, Mathematics, User Experience Research)