Welcome to the Sitefinity Forums, we would be glad to help.
Sitefinity is a platform that provides a lot of functionality out of the box, but also allows you to extend the core and develop on top of it. N-tiered architecture is usually defined as a developer concept, where you separate the different stacks into layers. The classical example is a 3-tier application, with separated data access, business logic and presentation. If this is a scenario that falls into your definition of "n-tier", here is how Sitefinity handles it:
It uses a database which is accessed through providers. You can dynamically change where each provider gets data from (for each feature separately), enable multiple such providers and implement custom ones. This is valid for all content in the CMS.
The business logic is handled by widgets (ASP.NET controls) which you can use on the pages in the CMS. Each widget and page has a template which form the presentation layer. The templates can be used from memory, or stored in the database or filesystem.
If we take deployment out of the picture and only talk about the architecture and development with Sitefinity, we already fit the "n-tier" definition. How you deploy the project is another matter. We try to support any way that you can deploy a normal ASP.NET application. Your database may be on one server, while the Sitefinity application (handling business logic and presentation) on another.
I think that deployment scenarios vary wildly and we cannot strictly recommend which one to use. That decision depends on the hosting you've decided to use (Virtual Private Servers, shared hosting, cloud, your own infrastructure). We would be happy to provide more detailed feedback if you share details about your live environment. If you have not yet decided, you can have a look at our hosting partners.
More information about the architecture and deployment is available in our documentation in the following topics:
Sitefinity can handle almost any deployment that fits into the ASP.NET / IIS system. Let us know if you need further clarifications on any of these or if you have questions for a specific server setup.