They could have done so before the war already. Just like technically Saudi Arabia would use it's oil wealth to become a bigger version of the UAE, instead of the sorry state it is. What's lacking in both cases is the people in power wanting to do so. After a successful seccesion the planter aristocracy still wont want to become captains of industry nor allow upstarts to compete with them for dominance.
The North was quite capable of feeding itself during the Civil War, there's no reason for them to buy imports form their rivals instead of continuing to do so afterwards.
See my first point. There wont be the necessary will to become a industrial or trade power.
Yes it was. What changed though, was that Britain started growing it's own cotton in Egypt and India during the Civil War. Originally fuelled by cotton demand due to the blockade, but with British Abolitionism and the war on slavery being in high gear, there's no reason the Brits wouldn't continue on developing them to wean themselves off their dependency of slave cotton.
Egyptian and Indian cotton would do to the CSA economy, what fracking is doing to OPEC.
Whilst Egyptian cotton was high-quality and led to the industry there developing and cotton boom that lasted until around 1877, the Indian cotton was less than ideal for the spindles of the British textile mills. The Surat cottons were unsuitable and the bales often were full of stones and other impurities leading the spindles to break. In addition the Indian cotton fibres were short leading the yarns to break and required extra humidity leading to a large decline in output. In France however, the slower spindles there were able to handle the Indian cotton.
Also the following quote is a bit of an anachronism
"there's no reason the Brits wouldn't continue on developing them to wean themselves off their dependency of slave cotton."
It makes the assumption that the British government played a major role in developing the cotton industry. During this time, the British government intervened very little in the economy. British textile mills were going to buy cotton wherever it made the most economic sense. If cotton farming develops elsewhere, it will be because the free market dictates it. The 19th century is not the 1980s where sanctions were applied to countries. Brazil kept slavery (much harsher I'll add) until 1888 and Great Britain was that country's largest trading partner and largest foreign investor.
Raw cotton and cotton yarn remained the United States's single largest export until 1937. Even in 1913, 61% of the world's cotton was produced in the United States. I posted some of these figures below, showing just how important cotton still was as late as 1913. It clearly shows that cotton is nearly twice as high in export value as the second largest export (iron and steel).
List of Total Leading Exports from the USA in 1913
TOTAL $2,484,018,292
Raw Cotton $575,488,090
Iron and Steel $294,435,060
Breadstuffs $203,391,856
Meat and Dairy Products $157,486,469
Fossil Fuels $149,316,409
Copper and Copper Manufactures $144,909,117
Wood and Manufactures $114,777,513
Coal $67,209,514
Tobacco & Tobacco Manufactures $59,693,800
Leather and Leather Manufactures $59,994,68
Cotton Manufactures $55,536,267
Automobiles $35,453,643
For the U.K, Germany, France, Italy and Japan, cotton was their single largest import from the USA in 1913. Of the total cotton produced in the USA, 54% was destined for export abroad and another 25% went to Northern States.
Share of World Cotton Production in 1913
CSA 61%
India 17%
Egypt 7%
China 5%
Russia 5%
Brazil 2%
American cotton as % of cotton used in manufacturing of the leading textile producing countries in 1913
USA 90%
Great Britain 62%
Germany 61%
France 54%
Austria-Hungary 50%
Italy 64%
Russia 23%
Japan 17%
India 2%
Also, the cotton exports of the USA totaled more in value than the total exports of several other primarily commodity exporting countries. For comparison's sake I have added the figures of exports to the USA, as textile mills in the northern states overwhelmingly used southern cotton.
Total Exports in 1913
CSA Cotton Exports $771 million (includes exports to USA)
USA Cotton Exports $575 million (cotton exports only)
Argentina $485.5 million
Canada $393.2 million
Australia $382.1 million
Brazil $315.2 million
Cuba $165.2 million
Mexico $149.1 million