After reading a couple of times your scenario I will take the chance to say that what you need is a CRM like Salesforce fully integrated into your eCommerce or the ERP that you are using to manage your stock and sales.
Having all that interconnected I would say that we have the data of the sales and stock availability and then you can automate several things from Salesforce as well as your sales team can proactively make a decision and have all the communication of customers + orders, vendors and partners.
This covers all sales process from multiple channels now talking about marketing we may have 2 options or you use the basic marketing options available in Sales Cloud a solution within Salesforce or go full fledge integrating Pardot which is the B2B marketing automation tool of Salesforce "this is in the case you want to develop your B2B marketing strategy of the brand.
IF what you want to achieve is on the B2C side with customers and clients then you have Email Studio + Journey Builder a bundled solution of Marketing Cloud.
Did I say that all is integrated into Salesforce? yes, absolutely that means that is the same data across all solutions with the respective security and permissions layers per each dept and role to see and do what is correspondently avoiding duplicates and wrong misusage of the customer data.
So far, how I would address it from my experience if interested we can talk more if I have more details and requirements from your side.
Feel free to contact for further analysis and happy to help in any way.