You should find a local field and see some of this stuff fly, and see what you might feel comfortable with.
Ron S. above has some really good advice on the steps normally taken, and he also points out that not everybody needs to do every step. Depends on the pilot.
I would not worry about getting my turbine wavier yet. Get a nice DF and see how you like it.
Personally, I do think a DF ought to be a prerequisite for a turbine wavier. Only a DF has all the complex systems that a turbine might have. As far as the sign-off goes, it's up to the CD, totally. If the CD has seen your other models, and feels like you know all the systems, and feels good about signing you off if you are demonstrating with a simple propjet, then what's the problem? It's up to the CD, and they need to make a JUDGEMENT call. It's up to them to judge the overall picture of how you fly, build, and maintain your aircaft, and whether or not they feel you are ready.