Is it a good idea to start with kinda hard execution?

Well, my head holds a lot of ideas about books I want to write, and I noticed that most of the "better" ones I keep reviewing and adding a story points but I never truly wants to start them because it seems to be really hard to write for a debut. (First draft.)

The problem is that the more Ideas I have the more complex they are, so basically I am cornered by my own imagination because I progress in making stories just by making them in my head.

My last idea is kinda different, it is not a story but a set of very weird characters that are supposed to be interesting for a reader and the book is supposed to be a readers way to find why are they the way they are.

For a story purpose, I decided that it is inevitable I have to make some chrono-shifts. (Time alternations.)

One of my characters should start with a start and end to an end.

One of them is supposed to be retrospective, starting at the end and finding what happened. (Kinda like Memento.)

One of them is supposed to start in the middle of her story which should be told to both directions.

The problem is that this execution seems really, really hard, but I cannot write short stories no more, and there is just no "easy" idea in my head.

So I am asking you what would you do, would you just say screw it and try your best at writing this?

ps. This one is different because when I create a story I know where it is going, now I created characters (I have like a 2-page outline of each.) and I wonder what would they do and how would they react to the story I have for them, which is just a bone, I have a lot of space for their voice. :D