Hi and welcome :)
For your first question, as usual with this question, it all depends what you wanna do. I would recommend C because I think that it gives a good overview of how it works inside, but obviously, it all depends on how deep you wanna know how it works.
For your second question, we’re white hats. You can take a look at the Code of conduct : https://www.hackthis.co.uk/conduct :)
