Google Apps Script for Inventory Management

I'm seeking an experienced Google Apps Script developer to automate my inventory and sales tracking across three Google Sheets.

Requirements:
- **Inventory On Hand Sheet**: Track inventory using SKU as the main identifier.

- **Sales Sheet Automation**:
- Automatically subtract inventory from "Inventory On Hand" (Column C) when a sale is moved to this sheet Sales, using SKU as the main identifier.

- **Completed Sales Sheet Automation**:
- Move items from the Sales Sheet to the Completed Sales Sheet when the delivered date (Column I) is 15 days older than today's date.
- Even though rows will still be visible on the Sales Sheet for reference, I want them removed and only displayed on the Completed Sales Sheet.

- **Error Handling**: Log any errors in a separate sheet.

- **Execution Frequency**: Script should check for sales to move to the Completed Sales Sheet weekly.

Ideal Skills and Experience:
- Proficiency in Google Apps Script
- Experience with Google Sheets automation
- Strong problem-solving skills
- Familiarity with error logging in scripts

Please ensure that the script runs automatically in the background. No manual button required.