What to do to get highest possible whp ?

What do you think I can achieve. Right now everything in the engine is completely stock

 

145/155WHP with a piggyback

 

Turbo is already running high boost so your going to be pretty limited without serious modifications.

 

Is it safe on the engine to drive for 150 km daily on speed over 200 km/h
Also how much would be the maximum speed.

 

You're going to be revving pretty high doing 200km/h. And if you're doing that for 150km that will be a pretty long time to be revving that high. I wouldn't recommend it. You'll probably want to change oil every 5000km or sooner driving it that hard.

 

94 miles at less than 4000 rpm is nothing for these engines , I just did a 1000 mile round trip running 3500 to 4500 rpm for 200+ miles at a time with zero issues. These cars are designed with autobahn durability and driving environment in mind.