So problem one was solved; I can now get materials to stick properly to the bed.
Now I want to print PLA without warping; so I printed this fan-duct:



Look at that smooth bottom!! Rest of the surface was perfect too!
After that I got some 'clicking' when changing filament,, but this was not hearable during extrusion (though I did think I saw some variation in thickness of the extrusion....)



On this part you see a lot of 'dots' and somewhat 'burned' particles... I think this has something to do with the clicking, so I stopped using this extruder, until I have cleaned it. If there could be any other cause for this than rubbish in the extruder please let me know!

And here you can see the fan duct in action;


I didn't have enough fate in 'just' the air duct on the extruders, because the energy needs to 'move' away to some other place inside the room. So I also added two 230-240[mm] fans on both sides, both blowing to the left creating a air duct.
I've watched the temp of the heat bed during a print and it remained between 23-27 degrees Celcius during the entire print! (Without the fan it would rise to 40 degrees Celcius and gradually drop as the extruder got further away from the build plate.)
This variation in temp is probably also due to the 'flow' with probably affects the readout device a lot, because most of the times the temp was listed as 24 or 25 degrees (room temp was approx. 24.)

For those interested: I've attached all three additional fans to a fan controller which is fed by a random 12V 1.5A adapter I had lying around (did some soldering.)

Does it work? (more images to come...)