It can boot with out that. If your device keeps boot loop , try disconnect the flex cable of your cam front and rear and try again. Only the dockconnector and battery attached to logic board and start your phone
You can use the original battery but it is better to replace it, because the backcover is already off and when you clued it back maybe after 2 month the battery needs to be replaced and you have to do it again.
Where did you get it from? So to see at the pic’s it is Genuine Apple screen ( i am 99,99% sure, these screens are used by Apple Genius bar when they replace a screen), maybe somebody with more experince can confirm.
Here you can find the back panel glass for iphone X, iPhone X Aftermarket Blank Rear Glass Panel it is much easier to replace the hole back housing instead of the back glass panel. Ifixit do sell the back housing for arround $ 59,-