Show HTML content in editable text area

Question 1

Adding TinyMCE inside page is the trick.

Question 2

check this out... I put it in Console, so it would be easier to undersand:

using System;
using System.Net;

class Program
{
    static void Main()
    {
    string a = WebUtility.HtmlEncode("<html><head><title>T</title></head></html>");
    string b = WebUtility.HtmlDecode(a);

    Console.WriteLine("After HtmlEncode: " + a);
    Console.WriteLine("After HtmlDecode: " + b);
    }
}

Question 3

You can use jquery + jquery UI to transform a normal text tag such as "p" into a textbox, here i built an example:

http://jsfiddle.net/jXXgG/

$(function() {
var availableTags = [
  "ActionScript",
  "AppleScript",
  "Asp",
];

$("#tag").hide();

$( "#tags" ).autocomplete({
  source: availableTags
});

$("#tag").click(function(){
     $("#tags").val($(this).text());
     $(this).hide();
     $("#tags").show();
});    

$("#tags").blur(function() {
   $("#tag").text($(this).val());
   $(this).hide();
   $("#tag").show();
});

Question 4

Apologies if I've misunderstood you.

If you add a standard 'Richtext Editor' as a field's 'type' in the Umbraco document type - then you can access and edit the html tags within the Umbraco back-office, by clicking on 'html' in the top editor bar while you have your richtext field in focus:

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