1) Cities are a disease magnet. But they also are a innovation magnet. Allowing people to get together means a huge amount of innovation. It's the major way that GDP increases.
1) Not really, ideas still flow better when meeting in person. In addition, you would have to use massive government force to stop cities, which is both immoral and infeasible.
I think you are severely underestimating the impact of the internet and potential there for allowing the devolution of cities and how critical face to face is for conferencing ideas. As more and more people who grew up with instant internet communication come of age, who are used to conferencing ideas with text chat and the like come of age, I think you'll find that business' valuation of face to face will decrease, as much of that ideal is still driven by management that is dominated by pre-internet Boomers and GenXers.
Plus you're ignoring the sheer individual economic advantage devolution of cities grant that will help drive it as well. As Millennials finally start families and GenY, who grew up online, enter the workforce they will very rapidly find that there are serious economic advantages to NOT living in cities. Prices are lower, land is cheaper, money goes farther. The main thing that keeps people living near urban cores is balancing commuting time vs housing. If a person can do their job remotely, why wouldn't they move to a location where their salary benefits them the most? You also have to factor in cultural values, right now people are effectively forced to live near cities even if they hate it, but as remote working becomes more and more common you'll see thousands of people leaving urban areas because they dislike the culture or environment of the region.
Now, should this be top down mandated? Absolutely not. However, the government may well want to create some incentives to companies that encourage them to adopt pro-remote working set ups, as it would help economically reinvigorate rural regions which need help.
4) Bringing back Foreign companies isn't always a good idea, especially manufacturing. With China, sure. But with many other countries, free trade is a good idea, and makes things cheaper, which benefits everyone.
We need to figure out how to do international trade in a way that doesn't inherently screw over our own industries and citizens. Free trade, when all parties share similar legal structures and values, is quiet a good thing and allows smaller countries who are more specialized to bring themselves up (there's no reason that the US needs to be specialized when it comes to industry, we're big enough to be able to be generalist). Comparative advantage is a thing, but not all comparative advantage is actually equal. I tend to break down comparative advantage into two categories: natural and regulatory.
Natural comparative advantage is comparative advantage created due to things that are outside direct governmental control like environment, distribution of natural resources, or large scale economic measures like cost of living. These kinds of comparative advantage should be generally ignored when it comes to free trade and allow countries to leverage them to their advantage.
Regulatory Comparative Advantage, on the other hand, is comparative advantage created by direct government action. The most obvious example of this would be environmental laws and workspace safety laws. Basically if a government enacted law increases the cost of doing business in the US and so makes it cheaper to do the same thing outside the US, well, for THOSE laws we shouldn't simply accept free trade for. Rather, we should utilize tariffs to counterbalance those costs against gods made in locations that do not have similar regulations in place. Oh, this ALSO covers things like how some countries will artificially prop up their local industries to be more competitive with American businesses.
The thing is, a LOT of the comparative advantage the Chinese have had over US industries are in the second category. They've propped up industries with direct government support and they have considerably less restrictive environmental and worker protection laws. This may also apply to many other countries around the world. I suspect that once you remove areas of artificial competitive advantage from things, a LOT of industries may well end up being better located in the US or, at worst, Mexico, than on the far flung Pacific basin when it comes to trade with the US.