I'd make it lower, to be honest. 5/95 for Black Hole/Neutron Star, mainly because I am hesitant to have that much chance for wide-scale destruction of a black hole's extent. Remember, they destroy the hex they spawn in and have a 50% chance to destroy the hexes around them.
Also, for the supernova→nebula thing, originally the supernova automatically lead to a nebula, but that's not the case anymore. Would it be more appropriate to have it be 5/60/35, with that being Black Hole/Neutron Star/Nebula, or would it make more sense to have nebula formation be the more common result in the aftermath of a supernova? I may love scifi with all my heart, but my knowledge of astronomy is pretty much relegated to a single 100-level course I took last year.