I dont think you should think about 4 yrs down the line as youl probably want to change it 10000 times by then!
Also IMO 400 bhp is the maximum useable power the car (chasis etc) can handle, this is from various posts & reviews by people who have gone down this route. When I say useable I dont mean being able to use 500 or 600 bhp only in the dry, in a straight line, & probably only after 3rd gear.
If I was in your shoes I would think of 400 bhp as being the cars maximum, (especially if you want it as your daily drive) full stop & plan according to that only. If you want more power in the future I would sell the zed & buy something that was orginally designed with more horsepower in mind. e.g new Nissan GTR / Porsche 997 (S/GT3/turbo) / etc