Artillery is never at the front lines, and if they had to leave in a hurry for some reason, they would abandon the guns most of the time.

The guns are disassembled and then loaded into trucks, some had wheels on them which allowed them to be towed by a CCKW truck or half track, the Germans also used horses and mules to move arty pieces around. There were also self propelled pieces like the British "Priest" SPAG, which had their own engine and wheels to drive themselves around.

The guncrew may vary per gun type but the core elements are the" range finder"(not really sure of his name) who does all the math concerning the range to target, altitude, "sweep" range in the case of a creeping barrage, and the loader and his assistant who load and actually fire the gun.

Yes, the American crews were issued M1 carbines and M1911 pistols and the Germans were given walther/luger pistols and in some cases MP40 SMG's

As for the last two questions I would say the Germans had the best artillery early in the war but later it was the Russians who had the best, a lot thanks to the katyusha batteries.