I'm a native speaker but I can't even answer that question properly lol. Normally you use welches for nouns with the genus 'das' so for 'Das Kleid' you use 'Welches Kleid?' for 'Der Tee' you use 'Welcher Tee'. But if you want to ask someone which tea he would like, I would ask 'Welchen Tee willst du?' Sorry if that doesn't quite answer your question.
Exactly. Your answer is perfectly correct! But additionally the form depends on the case: Nominative, dative, accusative. Nominative: welcher = masculine singular, welches = neuter singular, welche = feminine singular + plural (all genders) Accusative: welchen = masculine singular; welches = neuter singular, welche = feminine singular + plural (all genders) Dative: welchem = masculine + neuter singular; welcher = feminine singular, welchen = plural (all genders)