That would happen though as they would need to trade to realize an advantage of first discovery.
Malians typically traded with other Sub-saharan nations. It just exchanged its gold for desert salt before doing so to maximize the value of their currency. Their trade links would've caused them to spread the South American crops inland, along the Niger river, and to the Hausa states and Benin. While the New World crops would've eventually reached Europe, it wouldn't be enough reason in itself for them to sail there.
That would mostly need an ability to control new Empire administratively. Mali didn't really have it.
Sending a branch family to form a kingdom and formally recognize the Mansa of Mali as its overlord wouldn't require much, especially since taxes were generally only leveraged on traders. The developments would effectively be local, and based around linking the South Americans to the fruits of African trade. With those links in place, and with the Malian Empire providing the new kingdom with troops still directly owned by the Mansa, the new kingdom's legitimacy would be directly dependent on Malian support.
They could colonize New World, but it could easily secede and pit under question benefit of colonization. Especially because Mali was bad at global trade and had little contacts with Europe, it would have little incentive to control New World and continuously invest into it.
Mali
specialized in trade. It just focused on inland routes because those were the most profitable ones (The Volta, Senegal, and Niger rivers working with the Trans-Saharan routes made inland trade easy and incredibly rewarding.) They didn't need to trade with Europe (although they later would), as they were able to trade with the North Africans, East Africans, and Arabs to connect them to the Indian Ocean and Silk Road trade routes. As soon as they realize the benefits of trading in silver, it'll become a repeat of the gold trade. Nobody knows where it is, just that Mali has it. They might even focus on developing the inland kingdoms of South America to reap greater benefits from the trade before letting some leak out to the rest of the world, ingratiating them to the coastal Malian kingdom.
Nope. That's not possible.
They mainly fought off because they were at home and Portuguese were, mind you, thousands of kms away from bases. To have capability to fight same Portuguese in foreign waters, they must be much stronger than that.
They won because of their military tactics. Every time, it was about their ability to launch salvos of poisoned arrows faster than the Portuguese could launch their darts, and the fact that Portuguese cannons struggled to keep up with them. The cannons weren't even able to scare the enemy navies enough to prevent them from continuing to attack. Given the fact that the environments surrounding West Africa and South America are generally similar, I believe their tactics would remain effective in both environments, and that attacking them on the ocean would be unprofitable due to reasons explained in the next section.
Otherwise Pirates would be a much much more bigger issue to them than they ever were to Spain.
Pirates would have even less reason to attack the colonies. Silver wouldn't be exported as ferociously in the early years, as the main source of value would be in the crops and animal products. Minerals would only become valuable later, when less costly methods of obtaining them became commonplace. In the gold-producing lands, all Mali would need to do is keep them from exporting it, which is easy enough to do. They were already rich because of their own local gold supply. Using the gold as a backup would work well enough, but it would take a few hundred years for the gold fields of Bambuk and Bure to become drained enough to justify even looking to other gold sources within Africa, let alone the New World. This would also mean enslavement of the natives would be largely unnecessary, and Mali's American colonies would primarily serve as an additional source of goods.
To keep things simple: The colonies would export animal products, salt (until Mali claims Taghaza for itself), cocoa, and seeds. The traders would bring back goods traded from the mouth of the Senegal river, which are traded along the river and the Niger river to Timbuktu/Gao, where Malian gold is most valuable. This means Islamic writings, African fabrics, weapons, ornaments, horses, Arabic tools, scholars, and things like those. Pirates wouldn't have much to steal, and even if the Malians decided to trade their gold on the ocean (from Wolof lands to North Africa/Arabia) by using the new caravel design, and suffered from pirate attacks as a result, they would just limit the gold trade to inland routes, as they always had. This doesn't include the effect this would have on trade with coastal African nations to the south, who would inevitably be drawn into trade in and with Mali if it begins to use the ocean for trading.
This is a thing that happened ever since early ancient times though. It doesn't reflect development too well.
Seems to be directly tied to development. If you aren't participating in some form of globalized economy, the values of goods will largely be determined by local factors. The buildings you construct and the organizations present will be determined by local demands. Define "Development" if there's anything else to be said here.
The most important thing for urban centers is about population occupation and what they produce or contribute.
Which is where African and American cities were inferior to European, which in turn weren't as developed as some Mediterrean, Middle East and Asian cities for a while. Crafting was more developed there and less in Africa and America, which lagged behind.
I don't see what you mean. The Malians generally wanted for nothing. Food and clothing were abundant. Water wasn't a problem, and they traded heavily in worked bronze, salt, gold, tools, and writings. Could you give some examples of what you mean?