I'm making all my friends call me Nonbird now. You have no idea what you've wrought.

To answer all your questions completely out of order:

I have a sense for powers the same way I have a sense of touch or taste or sight or sound or balance. It works in all directions and through barriers, up to the same range as sight and with about the same loss of detail over distance. I know where people with powers are when they're nearby, and most of the time I can figure out what they do if I look at them long enough. 'Look' is a metaphor, of course, I used to actually squint at people but it only helps psychologically.

I haven't gathered detailed statistics, but I live in a fairly big city and I can go as long as a month without seeing any new powers, so the overall percentage can't be that high. Everyone I've talked to who knows they have a power and remembers a time when they didn't has said it came in before they were ten; I'm in the 'can't remember a time when I didn't' category. It always seems to be relevant to them in some way, although it's not always obvious until you get to know them.

"Storebought" powers are interesting. I know one or two people with them, but they're even more secretive than the little bird; they haven't told me much and they probably don't want me to repeat any of it. I can talk about the powers in the abstract, though. They're very easy to tell apart from native powers, and it's usually easier for me to tell what they do without getting up close. I've seen a few 'in the wild', so to speak; there was a mint who rode two cars down from me on the subway once, who I never saw again, and someone who walked past me in a mall who had remote viewing.

To know if the little bird's power blocked me, I would have to have looked at someone she was covering who had a power. I haven't looked at someone she was covering, powers or no, so it's hard to say. At a guess, though, I'd bet she wouldn't. Her power is very protective, and mine isn't harmful.

On the other hand, Kolya's unobtrusiveness hides itself just as well as it hides the rest of him. When he has it turned up, I'm as oblivious to him as anybody.