Arduino Current monitoring?

Hello i have a few Questions regarding Mains Power Current monitoring.

First question is i have seen a few Powering monitoring meters before and i could get one. But i thought i would take a stab at making one my self. So this question is What type of current sensors would i need for this. I saw a few on line doing searches but not really sure what one is needed. My Panel box is a 200a breaker box coming in. then smaller breakers doing to the outlets and lights. Not i know i don't want to monitoring the mains coming in my building. So i guess I'm monitoring after the breakers to the outlets and lights. Is there where the current sensors are going?

Second question is Don't i need 100v volt so i know what voltage 'm monitoring. the monitoring meters i saw have 110v into the meter box and the current sensors also connect to the meter box. So not sure how that works.

Last question is the accuracy on it. Would it be accurate enough? Or would i need something in between to make sure that I'm getting the correct reading?

Thank you for any advice i can get. This is a summer project I wanted to do.

Start at https://openenergymonitor.org/