Do i need studio monitors?

Hi fi speakers colour the sound.  So if you’re mixing and producing it’ll throw your sound out - you won’t be able to accurately judge what to do with eq etc.  Studio monitors produce a flattish response.  You’ll hear things that you won’t with average hi fi speakers.  Research extensively what you can get with your budget.  It’s all in aid of producing a mix that’s balanced and sounds good on a variety of audio media and systems.

Flat EQ. Your stereo likely has a slightly scooped EQ, so if you mix to it you will be mixing to that specific speaker response. Theoretically, mixing on flat EQ will make it sound good on a larger variety of speakers and headphones.