Power assisted Velomobiles will become a very popular for of transportation (when enough people wake up to the facts of global heating and environmental collapse).
Velomobiles have an efficiency of 40 miles to 85 miles per kilo-watt hour of electricity, depending on the weight, speed, gears used, and hills you climb. As opposed to 3.7 miles per kWh for a full sized electric car. How can anyone not afford to own one of these minimalist vehicles?
Don't be discouraged by the pedaling, you don't need to pedal at all if you don't want the exercise. But it will give you better mileage. One man built a Velomobile that is charged by pedaling a generator rather than the drive wheel.
The paradox of improved efficiency while it may reduce the environmental problem wan at the same time lead to greater use of the technology and eventually result in more consumption and pollution. But if the size of the vehicle were lowered drastically from what we are used to, it would take a long time to catch up. That is one reason to keep the pedals on a vehicle that does not really need them because of the large amount of power. Think 'two person velomobiles'.
Contrary to popular belief, carbon fiber is not the strongest material for the body. The only thing that makes it strong at all is the epoxy. So you could use news paper for the sub-straight. But Kevlar cloth is the strongest material if stretched tight enough, but probably not the lightest weight. Some people use wooden door skins molded on the frame.
You can buy a kit to build your own, or you can get a really nice Velomobile ready made. But you do need to consider the right power system for these vehicles. Steep hills can destroy an a inadequate drive system.
If you must use a hub motor, there are some (see link below) that are much stronger than Crystal Lite, formerly known as the strongest. While hub motors can produce a longer roving range on flat land, they have problems with road shock and rain. Some have a disclaimer that their hub motors can't expect to last more than 7 years. So I would use a 1.6 hp Mars 909 motor and a large rim pulley, just to climb our steep hills with two adults and/or cargo up to 600lbs total combined weight.