If you already know how to work on a bike and you are certain that the frame's geometry can handle the specific components you picked out, it's worth doing for modularity's sake. You won't save much money like you would have a few years ago, but you can upgrade the battery five years from now when they're much better and yours is starting to go out. Apart from fitting the components you really need to consider if that frame is strong enough. Ebikes experience a lot more stress from weight, speed, and vibration. Cheap components and ones made for manual bikes will be much more likely to fail, and at ebike speeds that's potentially fatal.