How can I estimate what will blow first - PTC/TVS protection combination or my IC
I don't think using normal PTC will give us a well predictable behavior. The thermal time constant given by datasheet is referred to zero-power conditions. Is behavior is determined by too much factors (ambient temperature, voltage applied, etc).  

Why dont use a fuse? Maybe a resettable fuse (PPTC, I think you means this device in the question), that generally is little slow compared to fast-acting fuse, according to Littlefuse specification (see "Time-Current Characteristic").

Or better, why not an overvoltage crowbar?


  3) Whats a good starting point to understand [...]  


Some useful links about thermistors:


http://www.vishay.com/docs/33016/engnote.pdf
http://www.littelfuse.com/products/resettable-ptcs.aspx
http://www.avx.com/resources/technical-info-papers/circuit-protection-emi-filtering/
AVX about PTC (interesting for current-time characteristic)


And about TVS, Littlefuse and Vishay sites are a good sources of informations.