Hey Wilo-
Good progress, looks like it's coming along nicely.
Your problem with your pics is light- specifically, not enough of it. You're shooting in full auto macro mode, which is good, but to capture the image, the camera is adjusting itself to shoot in a 'low light' environment. This means it opens the shutter for a long time (a significant fraction of a second)- and if the camera is moved at all during that time (as it ineviably will be if it's being hand held), the result is trailing/streaking. Your pics will come out fine, as soon as you put a bit more light on the subject you're shooting. The camera will recognize the additional light, and shoot quick enough exposures that you can handhold the camera. Using the timer will make no difference, unless you mount the camera on a tripod, to keep it still. Make sense?
As for the chassis, paint the whole thing yellow, then do the black. Tamiya laquer is very thin paint, and there's really no advantage to masking for your initial color.