Modern challenges of E-commerce

Nowadays customers are able to switch seamlessly from one device to another or from the brick-and mortar environment to the web. Customers want seamless, highly personalized experience. How to build this seamless customer experince that will allow you to satisfay customers? What would be the impact on your business? How do we control omni-channel sales? 
How to create personalized offers? How many customers should be in one customer segment?