Password-Protected B2B Shopify Setup

I’m launching a strictly B2B Shopify store that will sell physical products only. Access must be locked down: every buyer registers, I manually approve the account, and only then can they enter using their unique password... (Budget: $250 - $750 USD, Jobs: API Integration, eCommerce, Inventory Management, Shopify, Shopify Development, Web Design, Website Design, Xero)