The cost per mile is a difficulit one. You have done it using a price of 13.5 cents/kWh, the national average. However, there is no DC fast charger I am aware of that is remotely close to that price. Tesla Superchargers recently came down in price but typically range from 28 to 45 cents, but these are at best 250kW chargers. Megawatt chargers can't help but cost more, a lot more.
At 50 cents/kWh you would pay 85 cents/mile for electricity. A modern diesel semi is required since 2014 to get at least 7.2 mpg, and at $5/gallon that's only 70 cents/mile. Some get better. The Tesla Semi needs below 41 cents/kWh to break even with diesel.
This means the Tesla semi and other electric trucks are going to need to source much cheaper electricity. That's a tall order. If they imagine pulling a megawatt between 3pm and 9pm, it's not going to happen.
A single operator can drive only 11 hours/day. So that does allow slower charging. In the 13 off-hours it could refill at 70kW, but in practice it will not go from 0 to 100, so for most refills good old 50kW will do for that recharge. However, in 11 hours it will drive more than 500 miles, so it will need one fast stop during the day, and a slower stop while the driver sleeps.
But even 50kW much below 40 cents is not easy to find today. Truckers will need to find a network of charging locations which can deliver that price on a large contract. The megawatt mid-day will cost more. The Tesla semi does not have a bed or 2nd chair for a team driver, but it could be modified for that perhaps. Then they will need to use megawatt charging all the time, but that's going to cost more than diesel.
The issue with the megawatt is that high power hookups are priced based on your max watts for a 15 minute period. You want to charge a truck or two you are going to pay a high price for your hookup. Enough solar to do that for the trucks that want to charge mid-day would be a major install. Enough battery to store the solar for later trucks a huge price. (Perhaps some day we will see truck stops at solar farms, but the drivers don't want to sleep during the day.)
On the other hand, the Tesla semi should need a fair bit less maintenance than the diesel truck to lower that cost.