You are mixing up ein/kein as indefinite article (in that case it would be in genitive case) with the indefinite pronoun. Remember, there has to be a subject in the sentence - the indefinite pronoun is the substitute for that. The forms of this indefinite pronoun in nominative case are keiner, keine, keines and keine. So it's nominative masculine: "Not a single dude speaks"
Yes. The only difference is that keiner keine so on... can show gender, where niemand can not.
Not the same job as with the no one and nobody. We use nobody for people and no one for things. It's a cheeky semi-insult to address people as no one. "Nobody can beat me up" sounds respectful and educated, where "No one can beat me up" is a small bit insulting and unrespectfull.
To me it is sometimes. I have lived in bavaria for 7 months now and though its easier for me to tell the difference because I am more aware of the grammar, it still is difficult for me to tell. And you can get away with just kind of mumbling the end because they do sound very similar. Like the difference, at least for me, with lieben and leben.
It can help if you are to watch German NEWS and feel the (slight) difference between these sounds. The slight difference is that in words ending in R, that R is formed somewhere at the base of the neck and it is actually a soft echo; just like the French pronounce sometimes their R or a British the R before a final consonant.
It should be "None speaks" which is identical to No one speaks. None speak is grammatically incorrect, since None is singlular. However, Duolingo marked "None speaks" incorrect as well, even though it is correct. I have submitted a report.
In English you cannot say no one talk. "No one" is speaking about one person, so it is singular. It's the third person singular, like he, she and it. He talks, she talks, it talks. I talk, you talk, but he talks. Or one talks. Or no one talks. It's the same with nobody. You have to say nobody talks.
None speak does make sense as the word "none" can take on either singular or plural meaning and the verb matches: http://data.grammarbook.com/blog/singular-vs-plural/none-were-vs-none-was/