The simple answers are, to my knowledge more or less worldwide:

> My assumption was --
> a) buying a [music] roll gave me performance rights;

No.

> b) any copyright expired 50 years after the performer's
> and composer's death;

No, 70 years.  Also, an arranger might be in the list.

> c) postings could be made if there was no commercial gain;

No.

Regards,
H. M. Mueller