Yes, you are right about "so". I misspoke. I should have said that "that" was short for "so (understood) that"
"Thus" would be an adverb. "That" as short for "so that" is the subordination conjuction.
Das ist sehr schwierig.
Yes, I know it's hard, but I think it is doable. When I can, I'll see what I can do.
Incidentally, the dictionary says that "only" can be an adjective -- like "few".
I didn't look up "nur".