For 1) you are correct. To decid whether the friction losses are important to you or not you should calculate the friction losses. There is a calculator here: Tool Box. At 13 gpm the difference in head due to friction is about 10 psi between your 1.25" and 1" pipes.
2) is true, neglecting the friction loss above, which isn't a bad approximation.
3) since the Grundfos is a turbine pump you might exceed the shutoff pressure here.
4) Yes, if the well's dry the static head alone will go over the poly pipe's rating.