Nationalist China would not be free market Hong Kong. There would be state owned enterprises and an activist government. But there would also be lots of private enterprises, and it would be open to foreign, especially US, investment. Taiwan was considered one of the original Asian Tigers even when Chiang Kai Shek was still ruling the country. A unified Nationalist China would not be as economically well off as Taiwan. There would be far more entrenched poverty, a vast peasantry, and less infrastructure. But it would better than the PRC, and its economic growth would reflect real wealth creation, not dubious Communist economic statistics.
Nationalist China would not be neutral in the Cold War, but side with the United States. Chiang would be less concerned about ideological issues, and more with power politic ones. The fact is that the Soviet Union is a threat. The US is a source of aide that has strong ties to China (through Christian missionaries, international trade, the WWII alliance, the China Lobby, and the Chinese diaspora.) Chiang would rely on American strength to protect China from the Soviet Union until China was able to stand for itself. Nationalist China might be a troublesome ally at times, but no more than France was. Nationalist China would likely have lots of problems with the European colonial empires, but that doesn't mean much conflict with the US. Instead, the US would cooperate with China so that the newly independent nations in East Asia would be part of the new postwar international system.
The Soviet Union backed the KMT because the KMT was the only force capable to holding China together against the Japanese who were virulently anti-Communist. It was not because Stalin liked the KMT. Likewise, Chiang accepted help from the Soviet Union because he would have accepted help from anyone at the time. Saying Chiang wouldn't support the Americans because of past Soviet aide is like saying Chiang would never have declared war on Germany because of the earlier help Germany gave China.
Nationalist China would have lots of issues to overcome. Chiang would eventually need to turn on the remaining warlords and clear out corruption. This was something he always intended to do, but never got around to it before being exiled to Taiwan. But he knew of it and always intended to do something about it. He misjudged its importance and delayed too long. Most of the things he needed to do was quite simple (like institute a centralized payroll for the military or install independent auditors in the provinces). Chiang himself was not personally corrupt, so he had no reason to perpetuate that. Some of his in-laws were pretty bad, but while I don't think they'd ever be prosecuted, they'd likely be stopped once everyone else was.
There was the issue of land reform. This would be more tricky than in Taiwan as Chiang would have a lot more peasants and a lot less money (relatively) to distribute land among them.
Likewise, a Nationalist China would deal with the same kind of issues the pRC is dealing with now in terms of uneven development of the coastal regions versus the interior provinces.
In terms of democratization, I don't see Chiang giving up power. But I do see a fairly liberal press and local elections. He didn't think China was ready for democracy now, but he seemed fairly sincere that he intended to prepare China for it.
There are many myths surrounding Chiang and the KMT. While they have a semblance of truth, most of the ones Americans learned after the war were simply false. Nationalist China would not collectively be as developed as Taiwan today, but I think an extra 10-15 years of growth would be about right with about the same level of democratization.