At first are you living in Finland or where are you located? I'm assuming that you are looking for upgrades to W205 series C-class.
Is your car diesel or gasoline powered? That sets some limits to engine upgrades and of course how much are you willing to spend to car. I'd also like to point out that current legislation have recently changed here that especially diesel powered cars will be inspected more closely regarding engine tuning and emission equipment modifictions. If authorities notice something you could get very big fines. If you end up installing some chip etc. do you homework who will do the software and how the software is done and what it will chance in engine management.
Then regarding the suspension work H&R, Eibach and Bilstein are quality manufacturers. I think there is a discussion about stiffer/sportier suspension modifictions in W205 chassis.
About the bodykit, AMG is nice. I don't know the availability of the bodykits or how bolt on they are in that particular model. Searching from the web will help you. eBay might be the best place to search parts if you're looking for OE parts. Condition of the kit will affect the pricing and it will require some professional installation and most likely new paint job.
What comes to wheels if you are looking for comfort ride I'd stay in current wheels. Roads are so poor condition here so having bigger rims will cause issues. If you end up chancing wheels I'd personally go with AMG/BBS etc classic tuner wheels. It is all about how much are you willing to spend and what are you looking for.
I have used Continental tyres with no issue. They are not the cheapest ones but they have gain good grades in magazine tests.
No offense, but why don't you just change the car which already have the desired options instead of doing modifications to your car? Most likely it would come much cheaper to buy/chance new rather than do the all modifications by your own. Of course if you think that doing those modifications are your hobby then it is a totally different thing. Keep in mind that doing modifications may ruin the value of the car.
These are my 2 cents. Hope that helps a bit.
Cheers,