@Presidential dictatorship, etc, leading to state successions
Yes, absolutely.
@AfroAm revolter state
Er... Frankly, don't see it happening, though it would be a great story.
You'd need to expand the proportion of slaves way beyond their historic level by reopening trade with Africa, but many of the slave owners themselves had an interest in maintaining the ban on transatlantic importation: it kept the value of their 'property' high. And I don't know what the practical limits would've been: at some point, there'd be no use for further slaves since every plantation would already be working at capacity.
@Constitutional right
I don't know what's contentious about it. The South lost, so the Supreme Court mentioned in passing that it had been an treasonous rebellion based on... bupkis. If the South had (somehow) won, the North still would've clamped down on secession to prohibit the West from going its own way but the South would've certainly published plenty of judicial opinions and learned commentary about the rightness of its own course.
@Other issues
As Abdul argues pretty persuasively, the immediate cause of the secession was well-founded fear by the Southern socio-economic leaders that the North was about to force through a protective tariff.
My own personal wishlist would be to see tariff policy have an effect on POPs and foreign relations commensurate with its historical importance. (High tariffs bother aristocrats, farmers, laborers & all states, esp. UK, allies, and neighbors; low tariffs bother players, capitalists & possibly their employees.)