you have many different options when it comes to this, you can go d15b7/d16 vtec head (this is a Frankenstein swap where you put a vtec head on a non vtec block), or d16 vtec, or single or dual cam Zc its personal preference, but do not go for the non vtec motors such as d15s and certain d16s research use wikipedia it works the best to find this information
put on a turbo
There's only one type of 400 turbo.
The 14b turbo the TSI's come with stock.
Turbo, Ali or Musky
lime wire turbo
It depends on the specific car. Some will be undriveable without the turbo, but in any case it will be severely out of tune. With the turbo missing you can expect, at best, reduced performance, reduced fuel economy, and increased emissions.
the best Bmw classic is easily the bmw classic turbo
A turbo.
New Kids Turbo
That depends on what you are wanting. A turbo is more efficient but has a delay (lag) on accel. A supercharger does not have any delay, but is not as efficient.
No, only a certain range(size) of turbo will work(efficiently) for a 1.6 diesel at the rpm range, boost throttle response you want. Link below is to one of the best turbo calculators, IMHO.
The waste gate controls the boost coming out of a turbo by bleeding off exhaust gases/pressure to the turbo's turbine. By control the amount of gases/pressure the turbine see's, it controls the turbo's speed/pressure.