Hi;) Yes, if you say "mouichido yukkuci hanashite itadakemasuka" it sounds like you are talking with someone very important, so firstly let's modify it with "kudasai". It can be mouitido yukkuri hanashite kudasai this sentence is correct, you can use it;) but I also think that it is not perfect because in Japanese when you want to ask some action to other people you should better give them options but if you use "kudasai" it's polite but an order. So I offer you this sentence mouichido yukkuri hanashite moraemasuka? "moraemasuka" tastes like "could you...?" but we often use it and it sounds more soft, feminine, educated and without any aggression. You can use this form to any people;)

Hi! I'm not perfect in japanese but I usually use these phrase when speaking with my sensei: Mou ichido yukkuri hanasite kudasai. It seams to be not so rude:))