The only black I've tried has been from Octave Systems. It has proven a bit more problematic than some other colors, but I have gotten some acceptable results with it, generally better than what is shown in your photos. Firstly, black simply tends to show imperfections more than other colors. Secondly, I think its (presumably) high pigment level leads more quickly to nozzle clogging than other colors. Thirdly, it seems to "dry" more quickly than other colors, which I think can lead to poor layer lamination. YMMV.
The support material you're having difficulty removing is not "raft" per se, it is "dense support". The Up! software puts it underneath all horizontal surfaces, and yes, it can be really difficult to remove. Using Drew Petitclerc's fan duct which directs some air to the nozzle may help. I'm sure the adhesion of the dense support is also related to the specific plastic you're using - other colors or vendors' material may be different. It is not related to the vertical height adjustment. The vertical height adjustment only affects the very first layer of the raft. After that, the platform just drops 0.2mm with each layer.
I haven't really experimented with bed temperature or attempted to correlate it with difficulty of dense support removal. I just hit "preheat bed" while setting up every print I do.
I wish the Up! software provided more options for dense support that might make it easier to remove. Obviously, using one of the "raftless" printing techniques will take care of the issue on the bottom of your parts, but it won't help for other horizontal surfaces you might have.
Finally, try different orientations of your part - I think the one that you show in the photos might come out better if you were to flip it over.