My new system is now "finished". The past week I decided to get a better cooler and new power supply.
The cooler I had was keeping the CPU cool enough, also under stress, but needed a lot of fan revolutions to do it, so a lot of noise and I hate that.
The power supply I had was also good enough but almost 8 years old and I felt it would be stupid to potentially damage my new system because of an old PSU.
So the CPU cooler I bought is a Cooler Master 212 EVO and the PSU a Corsair RM650x. The PSU has a gold rating (meaning it is more efficient with low power consumption) and has semi-passive cooling. The fan does not run until the unit is under medium to high load. I was using 300 watt today gaming and only after about 10 minutes or so it started to turn slowly.
Also, with the CPU cooler and PSU I can now make a media center with my old hardware. I bought a second hand pc case for 10€ and it is now hooked up to my TV and I use it to listen to music. I used to do this with my 2008 laptop but it was begiining to struggle with 1080p .mkv movies.
So this is what my system looks like on the inside: (I am actually thinking about getting everything out and spraying the inside of the case black.)