I don't know if mine have any breast tissue in them or are just a bit fat, but here are my answers...
A little. Not much.
Yes, very much so, they're now an essential part of my sexuality. Yes, they get incredibly pointy and all the more sensitive.
Yes, absolutely. I love to have them teased, licked, sucked, pinched, pulled and even twisted (but NOT bitten, for some reason that just hurts nastily, although I do enjoy clothes pegs occasionally). It makes me horny as hell; I can be brought right to the brink of orgasm (but not quite to it). For some reason it also makes the lower halves of my bottom cheeks very tingly and squirmy, making me feel like a naughty boy who deserves a sound caning.
I got the odd comment in the school changing rooms, mainly about the size of my nipples (by which they really meant my large areolae), but that was only once or twice and thankfully I didn't find it upsetting.
Yes, I occasionally check for lumps.
Am more than happy to answer any other questions you may have.