[OS X TeX] Accented characters in Xe(La)TeX

[Dr. Clea F. Rees]

Could somebody point me towards documentation explaining the way that
Xe(La)TeX finds and uses fonts and/or typesets characters?

I'm specifically interested in a couple of things:

1) persuading XeLaTeX to typeset accented characters correctly when
using non-default fonts (e.g. ^W, ^Y, ^w, ^y, "W, "w etc. in
Skia, Venturis ADF, Hoefler Text etc. as opposed to Latin Modern);

2) identifying which font files XeLaTeX is using in a particular run
(pdfTeX gives at least some of this information e.g. it lists the TTF
or PFB files it used but I don't know how to get XeLaTeX to do this);

3) understanding how to work out how to access particular features in
OTF fonts e.g. OSF in Venturis ADF (as opposed to OSF in Skia which
seems unproblematic), for example.

I'd really like a pointer to some straightforward documentation.
fontspec and the font-info are not giving me the answers I had hoped
for!

Thanks very much,
cfr

(And apologies for having so many questions and offering no answers!)