I'm not changing the subject. You are trying to avoid a point that refutes your argument. Adding new states was going to be difficult for the Confederacy, and that would have abated the problems associated with territorial expansion.
To argue that a successful secession would not have led to war, is to ignore the warfare that had already taken place in Kansas; and it also ignores the fact that only the fraying bonds of union had prevented warfare both before and after that. Once those bonds were broken, the fighting in Kansas was sure to be repeated in all the territories.
Fighting took place in Kansas and Missouri because under the US constitution it was easy to add a new state, and so the political alignment of new states mattered. But with the Confederacy having a constitutionally difficult expansion process and no possibility of swinging a political majority by adding a new state, there would have been no reason for the violence on the frontier and no incentive for the Confederate government to get involved in such violence if it happened.
Difficult or not, the Confederacy clearly intended by its constitution to protect and even promote the expansion of slavery into both territories and, eventually, states. I think you overstate the supposed difficulty of getting the required congressional approval -- the Southern motivations for adding slave states to the Union would not have disappeared simply because the Confederacy was formed. (As an aside, the "two-thirds" clause is scattered throughout the Southern constitution, an apparent reaction to the narrow majorities by which their cause was being nibbled away. It evidently turned out to be a very serious hindrance to the Confederate government in their prosecution of the war....)
That it would be "difficult" for them in a more practical sense is beyond question: the chief difficulty being that they would be in competition with the North for those territories that would become states. In the end, it would have been nothing more than a different form of the Sectional Crises, which revolved around Southern attempts to admit new slave states to the Union, and Northern attempts to prevent it.
Given the certainty of competition, and the history already in-hand, it's easy to conclude that the "difficulties" of adding states to the Confederacy would almost certainly have included warfare of the sort that had already convulsed Kansas.