I don't think the governor actually wanted to kill them all, simply to make them suffer and take away their "safe zone" as otherwise he would have obviously killed more if he really wanted, he had the element of surprise, organisation, man and fire power. If his agenda was to kill them all then he wouldn't have left so soon.
Recoil has never been a part of this show, only Rick's handgun seems to have recoil
Also maggie doesn't seem to have the best shot as shown in the last episode with shooting Haley and again when under fire by someone who has the high ground (as well as the other guys shooting at them) it would be pretty difficult to get a good shot.
Rick didn't drop the hand gun, he kept it and used it against walkers as a melee weapon. He dropped the assault weapon as he had no ammo and carrying it would only get in the way, slow him down plus it's not like he could do anything with it anyway.
Yup that was a bit stupid, however, if it weren't for Merle and Daryl, they would have bit him, remember T-dog was able to hold two back for about 5-10 seconds before getting bit and he had a chunk of his shoulder torn out. And these walkers are rotting away, they are dead after all, so muscles etc. will be wasting away.
I would say that it is much harder to get "perfect headshots" when they are under fire by a group of people (with heavy firepower too, not just pistols......), of which they don't know where exactly they and how many there are, getting headshots on walkers is no problem since they are slow, can't attack/kill you unless they are literally right in your face thus you don't panic/worry as much.
Walkers have never been a danger by themselves or in a small group in the open but when in a large group enclosed somewhere i.e. like when they were taking the prison then that is where they are extremely dangerous.