Answer:
I believe that all the things you listed on the question helped Constantinople economically. The most important thing, however, is that Constantinople was located in a trade route confluence, connecting Europe and Asia. But the geographical, and architectural aspects were important too.
Step-by-step explanation:
You ask for a question related to the economy. Well, as the capital city of the Eastern Roman Empire, Constantinople was built in a strategic location. This city that received the name of Emperor Constantine I, Constantinople (or Byzantium, if you wish) it was one of the greatest cultural centers of the Roman Empire. At the time of its heyday, this city represented what left from the Roman Empire, especially because in the western division (which capital city was Rome), a huge fragmentation was in process since the 5th century. The location of this enormous city was between the Golden Horn and the Sea of Marmara, which created a safe place. But most important, Constantinople was located in a confluence of several trade routes. And the geographical conditions promoted safety for the city, because the invaders couldn't attack by any side beside the ocean, and the city was surrounded by huge walls.