Your weight, fitness, the hills you have, the distance you want to go, how much shopping or other stuff you want to carry and how hard you want to pedal all have a bearing on what sort of ebike you want to build.
Bear in mind that you don't need expensive lightweight stuff when you have a motor. Those sort of things can be negative factors because they inevitably make the build more complicated and eliminate some of the best options to give you a nice ebike.
If your specific goal is to make a lightweight bike because you have to carry it up stairs or manhandle it into a vehicle, that's a different matter. You can build anything for fun or a challenge, like those guys, who build unrideable custom bikes for shows, but I'd rather build something that not only gives me enjoyment when I ride it, but also provides a utility function to improve my life.
For long distance touring, you need a large battery (heavy), a frame with full air suspension, enough room in the triangle or on the downtube for the battery, hydraulic brakes, comfort handlebars, some way to carry stuff (racks or trailer). I can't see a carbon frame being any use at all unless there's something special about it or unless you're lightweight and super-fit, so don't want any significant assistance. You need to tell us more if you want valid opinions.