For soundproofing, use soundproofing materials--either constrained layer damping drywall, such as Quietrock brand or multiple drywall layers and Green Glue. Before the constrained layer drywall was invented, I used multiple layers on resilient channel. Lots of labour that can be easily short-circuited by just one wrong fastener, research shows.

you are correct....open cell is the cheaper, less R and higher perm (allows more water through) then closed cell. Closed cell will be a added cost, but would probably be worth it in the basement at least. Closed cell, in general, will seal up your entire house better then open cell, as well as add structural rigidity to your 2x4 framing making your house stronger. Open cell does not. Closed cell is not water proof, as it seems your questions are hinting toward. Cellulose is just fine for the attic, and going with more closed cell is a waste of money IMO. An animal can rip apart open cell just as easy as getting into cellulose. Besides, if something gets in there you have bigger issues anyway! Also, your roof is suppose to be water proof....not your insulation. If your roof is failing, you do NOT want a water proof insulation anyway. This traps water and allows wood to rot, thus a possible structural failure in your roof without you really even knowing. You may also be money and r value ahead to practice air sealing your walls with caulk and then using a blown fiberglass or dense packed cellulose in your walls. A side note...spray foams are THE most expensive possible way to insulate a home, and most cases you will never see a ROI compared to dense packed cellulose and blown fiberglass with air sealing especially in your climate. (note, I never mentioned batts).

I did read the info in the link. Previously i read the air space was needed to reduce ice daming. I thought the space allowed drying and, well, venting from the soffits. I thought in the warmer monthes the space absobed the heat and allowed it to vent through the ridge venting i would be installing before it entered the home from above. I read also that no airspace was also an option but that the spacing method was the tried and true method. ie. the easier method to reduce icedamming I was thinking the foil back could help with heat reflection but that the main reason for it would be low permanence (level 1 barrier). I am sheathing the entire home in 2.8 inch foam right to the roof line so i was going to try my best for an air sealed structure. This only leaves my rafters and rat tails for thermal bridging. I real would like to not remove my roof to add foam. As you can tell, I am not a pro so all this info helps me alot. I am trying my best, i want my home to ge great for my family.

Open cell polyurethane spray on the underside of your roof will be way below the minimum recommended R Value for new wood framed homes, according to the US Department of Energy. If you have typical 2x6" rafters, you will only be getting R20 vs. the minimum recommended R30. actually 2x6 rafters are 5.5" filling the rafter bay with 6" of open cell foam meets the catherdalized insulation standard. foam covers faces of 2x's to minimize thermal bridging. see pictures linked in my previous post. Plus, unless the job includes sealing all the openings into the attic from the exterior, you will not be getting the full benefits of the insulation. (See linked document.) document linked is promoting rigid foam sheathing to exterior of roof. OP is applying foam to interior of attic at roofline. when roofline is foamed the air and thermal barrier is now at the roofline not the attic floor. leakage sites that were problematic with insulation at attic floor are no longer sucking (negative pressure) from the conditioned space below. Only if you have those leaks sealed and use closed cell foam does spraying the underside of the roof make economic sense. open cell is used in hot humid climates. not closed cell. Unless you have HVAC in your attic, you will likely be getting a much better return by insulating the attic floor as suggested above. Unless being the operative word... 90% of homes in the south have hvac in attic. and ductwork in the attic. putting equipment and ductwork under the insulation (foam on roofline) allows equipment and ducts to perform. putting foam on attic floor still puts equipment and ducts in 130 degree attic. Spraying R20 under your roof on the Georgia shores and calling that fine and dandy? I wouldn't have anything to do with either of these contractors. If you want an impartial assessment, read the linked materials or contact an energy consultant in your area. Resnet is a good source for an independent energy rater. best of luck op