Need 3 custom modules

I need 3 custom modules done and 1 Task 1st task: I will need a developer to fix some bad code in current extensions. I hired a developer that did bad/not so good work, very poor job. I will need someone to go in there and fix 2 extensions. Also, I will need 3 custom extensions built after that. I will pay in milestones, say for instance, $250 milestones. You must have excellent PHP/MYSQL experience! 1.) Magento Synchronization Module to be built in Magento 2.x version for the Magento Admin to sync the Users, Products and Orders to external Application. The synchronization should be automated and can also be done with manual sync option. The sync module should have an interface for the web Admin where the URL, API key can be updated. 2.) Custom order module for Magento 2, Customize new page of existing Magento website, Upgrade categories, Test website and Payments 3.) We need a function to let customer with open order (not shipped yet), be able to (in frontend) add products that are in stock to an existing order. Use case: As a customer with an existing (but not shipped) order, I want to be able to add products that are available from the shelf to my existing order, by changing the order (only adding a chosen product) in my order page. We have a long list of work to be done on the website so anyone that can work long term, has expertise in custom work both front- and backend for magento 2 and are available for work straight away is more than welcome. We look for people (preferably teams with several Magento 2 developers) that can work right away, that we can trust and that we continuously can delegate custom Magento 2 work to. My Budget: $8,000 - $15,000 USD depending on how much work is involved in fixing modules