Not to the leaders of the Southern states.
There were incredibly few in those territories.
There weren't all that many in Kansas, either. That didn't stop slavery supporters from trying to bring it in as a slave state in 1857.
So? When the Southern states seceded they did so without making claim to any of the territories of the US. They obviously weren’t very concerned with the spread of slavery. It was only important for votes in the Senate so long as they were in the US.
In 1860 the Democrat Platform called for the acquisition of Cuba. When the Southern leaders met in Montgomery for their constitutional convention in 1861 one of the first objections made was to the proposed name - The Confederate States of North America. Delegates like Alexander Stephens thought it was too limiting. You better believe Southern slave owners were concerned with the spread of slavery and had the Confederacy won its independence then there would have been expansion plans to the south and in the Caribbean.
Yes to the leaders of the Southern states or at least most of them. Slavery was merely the pretext - economics then as now was what really drove things.
Yes it was a power struggle. Votes in the senate mattered a lot (for those economic arguments) so long as the Southern states were in. Once they were no longer in the US, there was no need for votes in the Senate and no concern with spreading slavery. The power struggle was over.
It was the era of Manifest Destiny and that held true for both the US and the CSA. Were there bound to be some expansionist sentiments in the CSA as there had been and still were in the USA? Of course. That’s imperialism/expansionism. That’s not some holy crusade to expand slavery. Cuba already had slaves.