Congragulations to Constantin on Mortal Instruments tv series
Major kudos to Constantin Films and Unique Featrues for not giving up on the TMI franchise. You actually took the time to consider all the angles and scrapped the idea of a City of Ashes movie knowing that you couldn't fit all the important details into a movie. Deciding to make this book series into a tv series was a fantastic and practical decision that quite frankly others that have done YA movies recently (*cough* Vampire Academy *cough*) would have done well to consider.
Rebooting as opposed to continuing the series was a smart move in order to correct the mistakes and omissions of the movie. To that end, completely recasting all the roles is necessary since this Tv series is a reboot and not a continuation to start anew and fix the problems of the past.
Because they are billing this as a 'high-end drama series' I'm assuming that that means it might be between 10 to 13 episodes, and not the traditional 22 episodes. The reason I say this is because they might decide to take advantage of every bit of their budget for each episode in order for every episode to be high quality. That would mean reducing the number of episodes to avoid any filler.
If I had to give Ed Deckter, the showrunner, some advice it would be to learn from the successful transfers from book to small screen (Game of Thrones, Outlander)and the ones with where there were mixed results (True Blood). The reason I mentioned True Blood as a mixed result is because while True Blood was wildly successful the later seasons starting with Season 4, I believe, were said to be by people who had read the books and others to be going down in quality because they started straying too far from the books. The other is even though I imagine him to be incredibly busy, is to sometime soon communicate with the fans on some platform such as twitter, facebook, instagram, tumblr, etc to show that he is willing to engage with the fans so they feel involved in this very exciting process.
It wouldn't be too soon for either Constantin, Unique Features, or either Ed Deckter himself to create a Mortal Instruments TV series facebook page so that the fans can have something tangible that they can communicate on about the show.
Welcome to Morganville. You'll never want to leave.