1. dont do it..it just isnt worth it...
2. insurance should WRITE THE CAR and replace it..
3. see other replies
4. if its just dents a good shop should be able to beat them out (mostly) then skim and fill them prior to painting...and if you think filling sounds iffy you should see how much filler 'quality' car makers use in the factory...
5. you dont trust a body shop...well all i can say is your using the wrong one..i.e your not paying enough, good bodywork guys are harder to find than good mechanics...and charge more!
6. unless you have CONSIDERABLE bodywork/spraying experience and equipment dont even think about doing this one yourself...

the question being am i qualified to talk about it..well probably not, but then again i do have some experience restoring motorbikes including the bodywork and I recon on 100-150 hours to prep, spray, rework, spray etc a bike panels (from better condition than it sounds like your roofs in!) and thats with professional tooling....for respraying a volvo roof your into at least $1000 worth of equipment...and you really want a booth and to use 2 pack...so your not doing that at home...