darui had the gourd, so I would say its safe to assume that the weapons dont work on the people weilding them. Kinkaku had the rope on his arm but his soul never came out, so while darui is holding the gourd it wont seal him...IMO
True. special weapons never affect their users unless specifically stated otherwise or unless the point of it is to surprise the user. The story loses its focus if the reader keeps thinking about the consequences of every single attack. Not that in naruto you would get many chances.
Side effects are secondary. chidori doesn't burn the user's hand and I, personally, never thought it should.
I have a wild guess.... Perhaps only "male" possessors of kyuubi's chakra have wiskers... Nothing else seems to make any sense... And how did naruto get whiskers?? Well he was born in the womb of a kyuubi host, perhaps some of kyuubi's chakra got mixed up with naruto before he was born....!
Just a guess though....
It's plausible that kishi only intended male jinchuriki to have whiskers. Wouldn't they look awful on kushina's rose cheeks? U_U I'd be disgusted. But what I thought was that only those who are immersed in kyubi chakra gain those traits. Like when naruto was inside a jinchuriki. The gin kin brothers also ate kyubi flesh while being surrounded by its chakra for two weeks. Jinchuriki have their biju chakra
sealed inside them. Under normal circumstances, it doesn't leak. And even small leaks aren't powerful enough to change physical traits.
I'm not sure about bee's ink, but it's different from naruto's marks, which were never mentioned in the plot, they're just a decoration. The initial story was about a demon fox, later changed into a boy.