Hello I have a Magento developer I have 3 and more of your expercies. I have 4 or more themes created and maintain Also full dedicated developer. I have known in Magento

1. Theme integration
2. Theme create
3. Theme customization
4. Extension creation and customization
5. third party extension creation and customization
6. API integration
7. payment gateway
8. another portal to connection and integration in Magento