Assuming you have not found the answer to this question.....
For each question.
Depends on your definition of useful or relevant. In most cases, knowledge that is generated is contextual to what it's been interpreted and used for, so you generally ask questions, like, for example, in terms of relevance: Which source is likely the most credible and less fallacious towards acquiring information. If you need useful sources on that, search The Hierarchy of Practical Evidence by Cedric Chin. For more scientific sources, there probably exists a much better meth
C.S. Lewis said "“I could never have gone far in any science because on the path of every science the lion Mathematics lies in wait for you.” I would say the lion was mostly calculus (though algebra skills are more or less assumed by calculus. At my high school and my son's high school, algebra and calculus were taught in same course). Even in stats, you can't move into the proofs for many theorems without calculus and I strongly recommend study of proofs so you know the real background to any theorem you might be applying (this is university level for most part).
I work in earth science and too many of my colleagues take fright at sight of an integral or partial derivative sign in a paper. Lack of calculus becomes a limiting factor so master it if you can. If you can't, make good friends with colleagues who can.
Assuming you have not found the answer to this question.....
For each question.
Depends on your definition of useful or relevant. In most cases, knowledge that is generated is contextual to what it's been interpreted and used for, so you generally ask questions, like, for example, in terms of relevance: Which source is likely the most credible and less fallacious towards acquiring information. If you need useful sources on that, search The Hierarchy of Practical Evidence by Cedric Chin. For more scientific sources, there probably exists a much better meth