Yes. In almost all dialects. The pronunciation varies between [e:] and [ä:] in different dialects though. My Stockhom dialect says [e:].
Being from Sörmland, i am pronouncing 'är' as 'ä' or 'ääh'. I suggest that if in doubt whether to pronounce a letter or not, pronounce it (it will just sound extra formal and usually never wrong).
That works too. There is some overlap but pojke is usually a little younger.
Yes and no, but mostly no. There is somewhat of an animate-inanimate distinction to en and ett, but it's not at all universal and regular. You'll find that en and ett simply has to be learned with the word.
pojke seems to be pronounced "poy keh" with the second syllable emphasmsized.
"Han" and "hon" are still used, but the gender-neutral pronoun "hen" is growing in usage, especially by the younger generations. This occurs due to the fact that Sweden is one of the most forward nations in terms of LGBTQ+ rights and acceptance, especially in gender expression.