I'm only a novice fiddler, but I'll take a stab at your questions.

Normally, no more than 2 strings can be bowed at once. I have heard of fiddlers who use a slack bow that sort of wraps around and can play 3 or 4 strings, but I have never seen one.

Bows are usually strung with horse tail hair. Synthetic hair is also available. The line (in fact the whole song) is fanciful, but I imagine that human hair could be used in a pinch. With enough rosin, nearly anything will sound the strings.

The fingers are placed on the fingerboard by feel and by ear. You learn the correct spacing and correct it on the fly by what you hear. The fiddle is one of the few instruments with true rather than tempered pitch.

Hope this helps!

Jeff