I need an opinion and advise from experienced ASP.NET people, what way to go.

Assuming that a developer has some practical background with HTML/JavaScript/PHP on one side and some .NET/C#/WPF experience on the other side. No previous hands on experience with ASP.NET - only theory and some read books on the topic.

The task is to build ASP.NET web site with User Managment functionality (user authentication, user account, user buying history, user points and so on) and E-commerce functionality with shopping cart, checkout and all needed for this.

Is it worth, i.e. will it be faster, more reliable and secure in the result to use a ASP.NET CMS system (for example Sitefinity from Telerik as declared developer friendly) to build such first site? In what case the learning curve will be more steep and it will take more time to achieve similar results?

Notes to take into consideration: 1) Price of the CMS matters not very much 2) E-commerce module should be written from scratch in any case (and integrated in case of using CMS) due to very specific requirements