Java backend for a B2B trade platform (catalog, RFQ, contracts, payments ledger, RBAC)

We are NEWMIND TECHNOLOGIES LLC (Tashkent, Uzbekistan). We are building a public B2B e-commerce platform for cross-border trade between two countries: company catalogs, requests for quotations, contract negotiation, payments, logistics, analytics. Languages: Uzbek, Russian, English (+1 more). Full technical specification (75 pages) is shared after signing an NDA. Scope of this job (backend): data model and REST/SOAP API; company accounts and roles (RBAC); catalog with categories and search; RFQ - offer - contract workflow with statuses and e-documents; payment and order ledger; logistics orders; notifications; analytics aggregates and exports; administration and reference books; audit log. Core modules (sign-in, roles, administration, reports) can be reused from our related project on the same stack. Required stack: Java 21, Apache Tomcat 10.1, PostgreSQL 16, Nginx, Ubuntu 24.04. OpenAPI documentation and unit tests are required. Frontend (Vue/Nuxt), design, integrations and QA are separate jobs. Terms: fixed price with milestones via Upwork escrow. The last milestone (15%) is released after acceptance by our customer; fixes of issues found during acceptance are included in the price. NDA and transfer of all rights to NEWMIND are required. Work is performed remotely. Final delivery: 20 December 2026. Please reply with: 1) price and timeline, 2) 2-3 similar Java projects (marketplaces, B2B portals, enterprise systems). Proposals are reviewed from 9 November 2026. Quality and relevant experience matter more to us than the lowest price.