This is a really cool question.
For Bilbo, I try to keep him fairly close to Tolkien’s original vision/inspiration: a crusty Englishman, or in this case Hobbit, who’s pretty set in his ways and has mutual culture clashes as a matter of course with his companions. He’s sassy, definitely, but I don’t want to put him into Sassy Gay Friend territory, and most of all I try to avoid the shrinking violet trope that people complained about in fics post-AUJ.
For Thorin, I try to convey the responsibility he feels he has to shoulder – the Atlas figure, if you will, without making him into a maudlin Christ figure or anything. He’s an educated prince, with extensive knowledge in warcraft, statecraft, languages, and culture; he’s not a bumpkin, and he’s just as sophisticated as Bilbo – if anything, Bilbo’s the provincial one. At the same time, I also try to get across that he has depth, especially regarding his fear and realization of mental illness.
Thanks for the ask! 🙂