Just for the record, as I'm imagine the poster knows, English does have traces of gender in it. Ships, for example, are "she." And most domestic animals or game animals have a very rich set of vocabulary, completely different words that express not only sex, but life stages, whether the animal is intact or castrated, etc. Thus, an intact male sheep is a ram, a castrated male is a wether, a female sheep is a ewe; an intact male cow is a bull, a castrated male is a steer, a female cow is... a cow. While, in cows, a freemartin is the female of a pair of opposite-sex calves--it gets a special name because it is infertile and masculinized.

My native language is Vietnamese and we don't have the grammatical genders :) I only know about this when I started to learn German :d

Chinese has no grammatical genders (although it does have three different pronouns for biological gender). As far as I know grammatical genders are unique to Indo-European and Afro-Asiatic languages, which English being a rare exception (there used to be genders in English, but not anymore).

My native language is Russian and Russian has three grammatical genders - masculine, feminine, neuter. We use genders not only with nouns but with adjectives and verbs as well. You cannot use any adjective if you don't know the gender of the word it describes: tall - I am tall. [Ya vysokiy - masculine; Ya vysokaya - feminine]. The tree is tall. [Derevo vysokoye- neuter]. They are tall. [Oni vysokiye - plural]. You cannot use any verb in the past tense without gender, it's like Passato prossimo in Italian but we don't use essere: andato - andata - andati. I fell. [Ya upal - masculine; Ya upala - feminine]. The tree fell. [Derevo upalo - neuter]. They fell. [Oni upali - plural]. I don't find it strange, I think that it makes English easier for learning and you don't have to bother about declination and genders in English.

https://en.wikipedia.org/wiki/Grammatical_gender will address your first two questions.