You can try to make flash games or text games with Java, C++ or any other programming language, but that takes a long time and you have to be experienced in programming.
Yes you can create your own Avatar character in the game.
You Could try The Sims 3. With the proper downloads from modthesims and Thesims3.com you should be able to create a great looking medieval avatar and castle. (heck, you could download one if you really wanted to)
no there is not but there is a game where you can choose the couple
Weegee!
Realmcrafter!
No, there are no downloads but you can hack into it and make your 'own' characters. (I advised that you don't. It can mess up your game)
You cannot create your own codes unless you know advenced calculii/hex.
When you start the game you get to create your own person.
On the game
Endurance - 2002 Create Your Own Game 3-18 was released on: USA: 29 January 2005
Endurance - 2002 Create Your Own Game 4-12 was released on: USA: 25 February 2006
Endurance - 2002 Create Your Own Game 5-11 was released on: USA: 18 February 2007