Thanks for the answers!
My point here is not so much to discuss the (dis)advantages of modular setups. I do see a lot more advantages than disadvantages for my specific use-case and am quite sure I want to go down that route. I am quite sure I want to use an X1 as a cheap, light, yet reliable and handy way to control Traktor. I am also sure that I want to use my Launchpad for the remix decks. I have heard enough success-stories of people using the same kind of setup live to know it can work well!
Now the real question is: is it reasonable to buy just a Z1 as a cheap 2 channel mixer for the two track decks, and use the mapping on the Launchpad to control the Remix decks volumes?
If I do assume a Z1 is fine for now, I am also limited about the clubs I can mix in, since I need a DJM900 or other Traktor-ready mixer with integrated Audio interface! A solution to that issue would be to have an Audio card like the Audio 8, and I can buy that only when (if) I ever need it. Does that feel reasonable?
If I don’t want to assume that a Z1 is fine for now, what is a good cheap 4 channels mixer I could get to train at home? All I need is 4 channels with EQ knobs/Filter knob/Volume faders, nothing fancy. Or is there a cheap 4 channel mixer that is Traktor-ready? Like a kind of Traktor Kontrol Z4 😛
What about the Behringer DJX900 USB?