How to read database connection string from web.config?

 System.Configuration.ConfigurationManager.ConnectionStrings["connectionStringName"].ConnectionString;

How to generate ASPX dynamically?

By Razor engine
http://razorengine.codeplex.com/

  string template = @"<%@ Control Language="C#" ClassName="@Model.Name" %>";
  string result = Razor.Parse(template, new { Name = "Classname" });