I have never used the complete Trangia system so I cannot answer some of your questions.
I bought two Trangia burners over forty years ago and made my own base and windscreen. Recently Clickstand created a light weight base and windscreen for the Trangia burner.
http://clikstand.com/home.htm
The simmer ring use after practice works quite well. The burners are more durable than many home made stoves and is very efficient in my experience. It is heavier than homemade.