The easy part first: OPERA :)
Don't jump in, stick your big toe in first! To see if you really like opera singing I will recommend ones I own.
PAVAROTTI'S GREATEST HITS
Has him at his peak (1980) singing the greatest Arias from the greatest Operas. This is a 2-CD set on the Decca label. On Amazon for $12.25!! This is great singing period! Placido Domingo has a few CDs of this type also. There is a reason excerpts of Operas are produced, because all you really need is the Arias. The rest of it, you have to be there to enjoy or 'get it'.
On the Soprano front:
Maria Callas, Jessye Norman, Kathleen Battle et al, have similar records. Not the whole Opera, just the 'good parts'. :) I have, and recommend:
Maria Callas -- LA DIVINA 3
To my taste, the Tenor Arias in Operas are much more enjoyable than the Sopranos.
If you like any of these, remember always get the 'highlights' of the Opera. I would start with the popular stuff like, TOSCA, CARMEN, and BARBER of SEVILLE.
A little Opera goes a long way with me, so I don't stray too far from the well known stuff.
Don't forget Opera on DVD. I just received The Barber of Seville with Kathleen Battle at the Met. Have not watched it yet. Will let you know.
Will send Classical recommendations later.
Cheers