1. 1900 Park Faire is on the 1st floor of the building closest to the monorail. It is in one of corners, close to side of the building near the monorail (not towards the pool, beach, resort, etc.). The monorail is on the 2nd floor. By the way, we stayed at the Poly for a week and ate here twice for dinner. A better buffet than most, with a Princess, and not very hectic.
2. Regarding the monorail, only the Resort monorail stops at the GF (stops at MK, Contemp, TTC, Poly, and GF). The Epcot monorail only stops at the TTC and Epcot, and the Express Monorail only stops at the MK and TTC.
However, you can take a boat (it is quick) from the MK. You can also take the same boat from the Poly, but it stops at the MK before going to the GF.
You can also walk from Poly to GF.
3. All depends on where you are before going to 1900 Park Faire and where you want to finish up after 1900 Park Faire.