Make sure you see a 12" before you order one unseen. They are big.
Re pyrex glass:-
http://www.skyandtelescope.com/howto...tml?page=2&c=y
Re eyepieces:-
Depends, of course. Read the many threads on selecting eyepieces. It will either become clear or even more confusing. What you can spend is a big factor in choosing. You can spend $800 on a single eyepiece. You will get an excellent eyepiece. But many sub-$200 eyepieces may give you very satisfying views. "DSO's" - what a huge range of objects requiring all the way from low to high power. Perhaps some of the Televue Ethos owners claim you can do all with one eyepiece. Most seem to recommend at least two and probably three eyepieces of different powers together with a good 2x barlow.