It will be interesting to see what the replies are here. From the reading i've done I have formed an opinion about just the very questions you posted.

#1- No it is not realistic. At least certainly not proven, as i've yet to see a chart or graph of anything that betters the performance of the engine. There are quite a few parts and claims that go with them, but none even come close to making them a decent value. $/HP

#2- I believe its a 3.2L engine from a SLK320... around a 2000 year model.

#3- NO.

#4- This car is a MB. they build them with a high state of tune to begin with, and leave little to add in later on by the owner. The compression and head design is about as good as it gets. Changing things like cam profiles and adding headers is just too expensive for the gains you can expect.

I own a 2004 myself, and i've used 3 different types of exhaust and intake mods, and not one has shown me any improvements what so ever as best I can test and tune at the track. Any other mods that could put some real numbers down just don't make financial sense, especially when the SRT and various other makes do so much better for much less.