3 genders (masc., fem. & neuter), 5 cases (nominative, genetive, dative, accusative and instrumental) and 2 numbers, sing. & plural

It's not even *that simple. There was an occasionally used dual number sandwiched in between singular and plural. It even had its own set of pronouns.

As for "natural" gender in English, The simple word for woman, wif, was neuter and the compound word, wifman (later to be worn down to our Modern English woman), following the Germanic rule of compound words taking the gender of the final element, was masculine.