The Black is a much more difficult river than the Manigotagan. It is best paddled in higher water but can also be quite dangerous in high water (dangerous take-outs and put-ins). There are a lot more rapids than the Manigotagan but there is still a lot of flat water paddling (though not much on lakes).
I would not recommend paddling the Black unless you have some experienced paddlers with you. The portages can be extremely difficult or non-existent. There are not many Black River pictures on the web but you can find some in my trip report (in Manitoba Trip Reports) and some older pictures here:
http://www.combinatorialmath.ca/rivers/black/black.htmlThe Black is not a maintained river like Manigotagan, Bloodvein, etc. The take-outs are not marked and portages are not maintained. As far as campsites go, see the pictures in my trip report. They are marked on a map.