"And finally - Texas, not to be outdone, wrote its own declaration."
Texas should have simply renounced the 1845 Treaty and reclaimed its status as a Republic.
Should have, but Texas weren't interested in becoming a sovereign republic again. They just wanted to be part of a nation that allowed them to have slaves.
Yes.
They wished to be a sovereign State with the sovereign right to continue the institution of slavery.
But, that is only largely true. :-)
Within the State there was much disgruntlement over the status of slaveholders and the role they played in secession. But, as I posted elsewhere, the men went off to fight to defend their State's sovereign rights. And many others, a good many of them Germans, sent their young men to Mexico to sit out the whole thing.