To answer the lighting/sealing the ceiling question .....
If you want acoustically sealed lighting cans:
1) Buy cans that are sealed (airtite) AND rated for direct insulation contact.
If you don't get cans that are rated for direct insulation contact and you pack the insulation on anyway, the fire department will be visiting you. Do NOT f**k around with this detail!
BTW, Home Depot/Lowes/etc normally do not stock cans that are sealed and rated, you normally have to get them from a "real" lighting supply house.
While you are buying the cans, also buy gaskets sets for them. The gaskets are thin vinyl w/adhesive (peal and stick - like a white bumper sticker) and are not very expensive (less than a buck). The gaskets bridge the gap between the drywall and the can.
2) Install the cans.
3) Pack the insulation around them tightly, behind and around, no voids. I prefer rock wool insulation for this job. It's meant for sound proofing and it will not ever catch on fire. (fiberglass insulation will burn if you heat it enough, I know by 1st hand experience!)
4) Install drywall and finish it, taking care to cut the holes for the can tight. (A Rotozip is worth it's weight in Latinum for this job).
5) Install gaskets.
6) install lighting trim rings which will cover the gasket.
This method isn't as good as a ceiling w/no perforations, but it works WAY better than standard cans.