Shopify Price Update from MWS

Here is how i see it working. I have multiple stores in shopify. I need the ability to connect each store with our app via shopify private API keys. Phase 1 Once connected the app will Pull all the products from the store to app database. (this is one time job for each shopify store). I should be able to add new stores when needed. Better would be if you put some code for each store. Also on each store, ASIN and price margin are encrypted in SKU field as Base64. Phase 2 This will be cron based running daily once. I will provide MWS keys for amazon. The app will take ASIN from database and update prices according to amazon. (here we will use same script we used earlier for opencart plugin). Here the app will also decide whether the product needs to be updated, deleted or skipped. Phase 3 In this final stage (runs daily after the first cron is complete), the app will update or delete products/variants based on the decision made in phase 2. Shopify has a query limit of 2/sec on each store so we can update multiple stores at the same time. Project should be able to handle 2million records and should be fast and reliable.