The classic mistake with calculations around this topic is assuming you need an equal amount of electric energy to displace the equivalent in fossil fuel. It's a broken assumption that you see popping up in a lot of places. Including reports by institutions that should know better like the IEA.

A classic example here is cars. A typical Tesla would have about 65kwh of usable battery. A gallon of fuel represents about 31 kwh. So, a 1 to 1 replacement would mean that Tesla would have about 8x less range than it actually has compared to a car with e.g. a 15 gallon tank and. pretty decent mileage of 16 miles to the gallon. Reason: a Tesla manages about 4-5 miles per kwh which amounts to about 250-300 miles range. Let's low ball that to 250. Meaning, you can drive about 8 cars more per kwh of electricity than per kwh of ICE car. Switching all road traffic to electric would mean we actually save a lot of energy. Maybe not 8x but it's going to be substantially less than what we currently consume in fuel for road traffic.

People underestimate how quickly this is going. Most commercial fleets are switching sooner rather than later. They have to, the cost savings are to large to ignore. That's most of the traffic on roads and it's not going to take decades.

Heating and cooling with heat pumps is the similar. A good heat pump that is installed properly should deliver a COP of about 4. Meaning you get 4 units of heat (or cooling) for every kwh you put in. A gas heater has a COP of slightly below 1. 1 is it's theoretical maximum. So switching industrial and domestic heating/cooling over to heat pumps is going to deliver some pretty significant savings as well. Mostly industries have barely scratched the surface on this topic. Industrial heating is mostly still based on burning gas or other fossil fuels. That's because gas used to be cheap and electricity used to be expensive.

Now that that cost has flipped around, companies are slow to adapt. But eventually some companies will start figuring this out and once they do it might save them a lot of money and make them a lot more competitive. And all that is before you consider using cheap off peak electricity when wholesale energy prices occasionally go negative!

4x-5x overall more electricity usage sounds about right. I expect it to be more because as energy keeps on getting cheaper we'll keep on finding new uses for it as energy prices keep on dropping. Assuming everything stays the same is not a great way to make predictions about the future. Things rarely do. But it's not that unreasonable to assume a 5x increase to happen over the next few decades. But it will cost us a lot less than our current energy spending. If we keep on going at the pace we are currently going we'll get there easily. And there are good reasons to expect things to speed up actually.

Solar cost will keep on shrinking. Especially in the US there is a lot of potential for improvements. That's because cost is currently inflated due to a combination of import tariffs and asinine regulations that mean installation cost is insanely high compared to other countries. Some of that regulation is courtesy of fossil fuel companies lobbying for this. But both are fixable problems. And more importantly, both are non technical problems. Meaning that international competition between countries (and domestically between states) will force the issue ultimately.