Completion of the site Opencart

Built an additional warehouse. Synchronized with the database. Now you need to configure and finalize all the stages of formation of the order.
1. On the product page on the website reflected on what warehouse the product is in stock.
2. After you add to cart, to finalize the withdrawal of goods from a particular warehouse.
3. If you select pickup from the warehouse where the product is no, add three days to delivery.
4. If the item is at least one of the warehouses, to make the goods available for sale and only in that quantity in which it is available. To synchronize the balances of both warehouses.

I can technically miss some moments. You need to modify the site so that the synchronization process, display, and checkout took place perfectly.

The cost and time commitment?
Budget rip as an example.