Insulating finished attic addition

[python01]

I just got my building permit for an third floor addition which basically will be attic with raised side walls. The ceiling will be vaulted.
I wonder what would be the best way to insulate the ceiling and knee walls? I was thinking about spray insulation but I think it is considerably more expensive than regular bat insulation so I wonder if it is possible to buy diy kits for spray insulation so I can do it myself to save some cash?
Also what venting would you recommend for this type of attic? both along the top of the roof as well as along the ceiling?
I am getting framing company to do the framing for me but the plan is to finish the interior myself so venting will be one of the more important aspects to tackle.

 

[nealtw]

Build the knee walls with 2x6 insulate with batts and add vapour barrier to the inside. A few strips of wood on the outside so the batts stay put.
The vaulted ceiling area should be 2x10 deep so you can but in battinsulation and still have room above that so air can get from the soffet vents to the ridge vents.
The space between the floor joist below the knee walls needs to be solid blocked and sealed, no air movement from the lower attic to under the floor.