I want to create a machine that will mine altcoins with revenue and for now my extra budget cound be an extra... 2000€-3000€
I ordered yesterday as well an antminer D3.
At best, your existing configuration could host 3 graphics cards with risers (you'd need to remove it from the case, however). You could attempt to use one of those PCIe splitter cards, which are often strategically priced at below the cost of a new motherboard with more slots, but those give mixed results on various motherboards.
If your budget really is that high, I'd recommend buying another motherboard, and, if you're not using your existing system for other purposes, taking some components from it.