What luggage carrying options exist for an e-bike
Many people who are hacking their own ebikes either use bottle shaped batteries that fit inside the diamond frame but are limited in capacity due to size, or they use some of the rear rack solutions pictured. Note that many of these rear racks are designed around the batteries and are a package deal. This arrangement isn’t ideal because they give your ebike a high center of gravity but sometimes you don’t have a choice. 



You could also try to emulate how the Sondors ebike has a hard triangular shaped box in the diamond frame that is quite capacious - here it has a bottle battery but many people have stuffed them with RC type square lipos: 





For your luggage, 60liters is a lot.... That’s a cube of 40cm (15.8”) in each dimension. You could split it into two panniers of 20x40x40cm but it’s still quite a lot. 

Have you considered pulling a small trailer? Or using a Dutch style cargo ebike? Both options have considerably more cargo space than a standard bicycle.