Open-Source SaaS Platform Customization & Integrations

I already host an open-source platform in a SaaS environment and now need it tailored so it follows my product vision more closely. The codebase itself is solid; the next step is to adjust it and bolt on the right integrations so the service feels seamless to end-users... (Budget: $3000 - $5000 USD, Jobs: API Integration, Backend Development, Flutter, HTML, JavaScript, Laravel, PHP, React.js, Software Architecture, Software Development)