They are both pretty widlely used but i find Guitar pro easier to use and better for writting seperate parts on. Power tab is good though. You just have to look. http://www.powertabs.net/ for power tabs http://www.mysongbook.com/ for guitar pro
You used to but most of those sites (that i know nothing about honest ) are being closed by the RIAA or MPAA. But yes you can. I just don't think it is very legal and would never do that ever
You need to get your hands on either Powertab or Guitar pro. both are very good tabbing software that also display the musical lines. Guitar pro costs money though so i would suggest looking at powertab first. Google will find it
The guitar in itself is not that rare although it is one of the best pacificas made. All pacificas however are very good quality and excelent guitars. I really wish i'd had the money as that one went for and absolute song.