Multi-Marketplace Listing Automation SaaS

My team currently has to re-enter the same product details on Vinted, Le Bon Coin, eBay, Vestiaire Collective, Depop and Facebook Marketplace one by one. I want to replace that routine with a single, cloud-hosted workflow: create a listing once, click “publish”, and let the system push it—along with images, price, size guides and hashtags—to every selected marketplace automatically.

Beyond the publishing layer, the platform should ideally gather each partner site performance metrics (views, saves, conversion, conversations) back into a unified dashboard so we can compare channels in real time and adjust strategy without leaving the app. The end goal is a polished SaaS product that other sellers could subscribe to, so modular code, clear API wrappers and a scalable architecture are essential.

To move forward I need:
• A short feasibility study that confirms each marketplace’s API or scraping constraints and suggests reliable work-arounds where official endpoints are missing.
• A phased technical proposal covering data model, queueing, rate-limit handling, authentication flows (OAuth, cookies or token refresh), and dashboard stack (for example React + Node + PostgreSQL, but I’m open).
• A pricing and milestone schedule—break down core integrations first, then analytics, then polish—so I can gauge overall investment and time-to-market.

Please outline any prior marketplace integrations you have shipped, the tools you recommend, and how you will handle ongoing maintenance when platforms change their rules. I’m ready to start as soon as we lock specs and budget.