I would try to get the graphics card with as much onboard memory as you can. The next would be a CPU with as many cores as you can afford. The third thing would be as much memory as your motherboard can handle. Now all that might be a bit out of your range, but I do not know the euro market for stuff like that, but that is when you start looking at trade-offs. I THINK the graphics card is the most important thing.
A suggestion would be to look at the recommended requirements for the programs you want to use and bring those to your teckies. They might not know about graphics, but they most likely are up on the technical side of things and can recommend specifics based on those requirements.
Just as an example, a year and a half ago I built my own (actually had a teckie friend build it for me based on what I wanted - basically for the same reasons as you) and I ended up with a 2gb graphics card, a 12 core i7-990 with 24gb ram and 2tb hard drive for $2500 (remember this was a while ago so prices for what is available will be lower in general). I was kinda hoping that it would help reboot my creative juices after a major heart attack gutted it, but so far I haven't had the urge to stretch it to its limits. I have tried some things that my old machine would stumble over and it was like night and day, but the spark just ain't there atm.
I wish you luck and happiness with your new toy to be.