Newborn night time feeds

So my newborn is three weeks old and has been gain weight well since she was born. I’m just wondering when I let her sleep at night and not wake her for feeds unless it’s been five hours. Is this okay? Also if I go to sleep myself when she goes down for sleep I get worried that if I don’t wake up to her hunger cues and wake up to her late hunger cues will this effect her majorly? Is it bad? These might be dumb questions but I’m just trying to work out when is a good time for me to get some sleep preferably more then a two hour sleep