Odoo Implementation

I have 3 x Shopify stores that share some common products and therefore inventory. I created an Odoo.sh database and added a 3rd party Shopify integration app. I have products downloading to Odoo OK. We also have the Sales, Inventory, and Invoicing apps. I am now stuck on making it work the way I want it to.

Please see our requirements below, and provide a rough price on how much for you to work with us to implement.

Phase 1
Shared inventory across 3 web stores (1 warehouse) - so if store B sells a product, store A and C show the stock level as reduced by 1
Different pricing - All 3 stores may have different pricing for the same product
Vendor purchasing via Odoo
Barcode scanning for inventory receiving
Barcode scanning for capturing serial numbers when fulfilling orders

Phase 2 (separate project to come later)
Adding Odoo CRM and capturing customer opportunities via web forms, manually entering, and emails.
Linked with Shopify so that customer history is complete from lead to purchases.
Adding Odoo Help Desk to draw customer data from order and CRM, and manage support cases to conclusion

Handled outside of Odoo
Accounting is handled by Xero integrated from Shopify
Fulfilment and shipping is handled by Shopify app