the fun begins
1) yes and no ; some are German large ring / some outside dimension large ring but use small ring barrel ( K KALS ) /1903 are different again
2) most have straight , but some bent
3) if you havent guess by now yes and No
depends on what your thinking of doing ; a K. KAl is mostly standard large ring with a small ring barrel , A Remington 700 barrel can be rethreaded to small ring and used on these
the triggerguard on some turks do not have the retaining screws so they can dress up the look of a sportier IF the stock has not been cut for military bottom metal
there is lost more information on differences you will need to do lot of digging