To directly answer the question Tesla has a calculator. (scroll down a bit)
The math is really fuzzy in the email because it assumes you get 25 mpg on electric. The 100Kwh battery pack the high end tesla has at .15c/kwh is 15*100 = 15 dollars. The Volt battery pack is 18.4kwh or 2.76 to go around 53 miles or 5.2 cent/mile.
As far as the grid goes, to replace all the gasoline cars in the US, it was roughly a 50% increase, but we have other efficiency things going on like flattening the grid, which should improve efficiency by 15-20%, and then you have other efficiency things like LED lightbulbs, tv's and pretty much all appliances get some savings these days, so it might not result in a huge increase in capacity. Obviously there are going to be localized areas that will need some upgrades.
The use case for EVs favors surburbia commuters. You can charge at home. For cities, and rural, it might not be a feasible solution right now. Cold climates aren't all that favourable, but the batteries keep themselves warm, so you do get decreased range but you aren't stuck either.
There are newer batteries in the pipeline that have about 2x density, weigh less, and last more cycles then the current generation, and work better in cold temps.
We just had to get the ball rolling. China right now is the world's biggest buyer of EVs. The US is like 1/6 of the world sales. We -may- pick up some ground now that the Tesla Model 3 is in production and being delivered now.
It wasn't a fast plan, as we have to undergo several generations of vehicles to cover the majority of the market. It just takes time to improve the tech, and recoup R&D costs and the new factory costs. But with the next oil glitch projected for 2022. It was important to get it started so you aren't sitting at the pump complaining about 4 dollar gas with no alternatives like we were in 2006. The cost of EVs wasn't actually projected to be the same as the gas alternative until 2030, but we are about 8 years ahead of projections for batteries.