Just remember to be different nowadays, you usually gotta have deep pockets because almost everything has been and is being done.
As for D-series, Im in the process of turboing my D15B pretty soon. My goal is to spend as little as possible on it. I have very little money in everything so far.
What you are saying is that you wanna spend alot of your money on the motor and turbo setup. Well doing that with a D-series, IMO, is just silly. DOHC is the way to go to make power. Plain and simple.
If I were in your position and had the money to do something, I'd rock the D16 for the time being and order a B16 long block. If you wanna spend money building a motor, do it to a dohc. You will spend just as much building one of those as you would a D-series.
Then you can also do more with a bigger turbo, making more power.
thats my suggestion. I've been in your shoes. lol I know how it is. Just take your time and dont rush a project. It will only get sweeter with time!
PS, nitrous is old news lol.