In reference to #1, check out this summary of module counts for each package manager[1]. The TLDR is that Java, Ruby, and Node.js dominate in terms of module numbers.
This is definitely an important question, but I do not have any data on it. If I had to guess, languages with package managers that are harder to use might have better quality. ie: npm is super easy to use, so there are tons of crappy node.js modules, while maven is harder, so the Java modules out there have more polish. Without data, however (how would you even measure it?) I cannot say for sure. Perhaps you could compare number of modules installed past some percentage threshold? If 90% of node modules never had more than 100 downloads, but Java had only 20%, that would be pretty telling to me and might lead to a reasonable weighting factor.
.NETs growth is only modestly better than Ruby or Java, but considering one should expect there are more opportunities for creating new packages, even just ones that copy what is already available in the Java ecosystem, I'd say this is to be expected.