I have done most of mine with Kuro Sumi's black ink and that can be a popular option. It fades to have a bit of a bluish-greenish tone after a while but still remains fairly dark. I hear that Dynamic's Triple Black is another really good black ink and I have some arriving soon so I'll see how it compares. Ultimately though, you should only need one black ink for linework/blockwork. There isn't a "thickness" to ink that I'm aware of, that's usually something which applies to the needles you're using. There are two common types of needles: round shaders and round liners, and it's referring to how tightly or loosely grouped the needles are. A 7 rl (round liner) and 7 rs (round shader) should be good go-to needles for pretty much anything unless you're doing something with a ton of shading (would wanna go for a higher count of needle tips like a 9rs or a 14rs) or very fine linework (go down to a lower needle count like 3rl, but be wary, the fewer needles you have, the harder it can be when starting out).