No, not all single words are "male", but for Plural, it´s always "die" (many plurals are genderless, please, don´t ask why "das" is not used xD"""""""""")
6000 if I´m right? But basicly I "only need" 3000 of them to read a newspaper - And I heared somewhere that the usual japanese teenager knows about 1500 (correct me if I´m wrong xP")
Usually I would just go with "Use the one which doesn´t sound strange" - but that´s a bit hard to tell to somebody who doesn´t know the language ^^""""
"Die" can also be used for "many things". In this case: "Der Hit" (1 hit(-song)) but "Die Hits" (all of them). It´s because there´re several of them on the CD
Knuckles in China Land (a pc game, I started to play it for at least 1 hour per day, seems good at teaching to recognize Katakana, Hiragana and some Kanji)