There are no true wrong answers in the human experience unless it involves 'kill them all and burn down the village', what happens in your bedroom or between your mates is on you guys. It's not like a school yard where a gal/guy you dated onces will point at you in a crowd and her/his friends will begin laughing histerically, and even if it did, screw her/him, she/he's immature.
1) Sure go right ahead, just dont make a big deal of it like at the end of dinner turn somber and tell her/him in the same tone that you'd tell her/him that you ran over their dog or got bone cancer.
2) If someone told me, I'd be okay with it, especially if I was dating them, I am a open-minded straight man and if she told me she was also in to broads, that'd be awesome. I cannot tell you the flip side because I am not a gal, ya know.
3) Wrong? No. For my experience there have been three types of bisexual I've talked to (could be more, this is just from me). Theres the "I hate my parents so I rebel" Bisexual, the "I am still finding myself out, experimental" bisexual, and then theres the "Tried, true, dyed in blue" Bisexual. I can honestly say I only have a problem with the first one, because no one ought to do these kind of things out of hate or to get a rise out of others.