I use a 12 gauge ALL the time. Hardly does anything to the meat at 10-15 yards with federal target loads (2 3/4" 1 1/8 Oz 7.5 3 dram) from wal mart. They drop easy and I don't have many that get away. I use a modified choke (half choke) so I don't hit them with more than 8-12 bbs.
I did find that a 20 gauge with target loads is a bit on the light side for the bigger ones. So I have pheasant loads (and old duck loads) for them ( 2 3/4" 1Oz of #4 shot high brass), but the game loads are $8.00 a box of 25 vs $3.75 a box for 12 gauge target loads.
And if anyone says that it cost to much for shotgun shells vs .22 I will just point out that I spent 15.00 for the small game license and 30.00 in fuel and a mere 15.00 for shells for the whole small game season. So shells are not that big a deal.
As for cleaning: Shirt and trousers method
What I do is cut off the head feet and tail with a pair of shears (I made mine from garden shears). Then I lift the skin up on the back length wise and slice it width wise across the back, I get my fingers under the skin and tear it toward the head and toward the tail at the same time. You will have to help it so they both come off evenly as the skin is about the only thing you can pull from. When you get it off it will look like a shirt and a pair of pants (hence the name).
Now that you have the fur off take a pair of scissors and poke it through next to the butt hole, try to avoid snagging any guts and try to get the scissors up to the chest cavity. You want to cut out the pelvis to get the butt hole removed without cutting it. Now use the scissors to cut from the neck to the belly and clean all the guts out, rinse the little rat off and your done.
I recommend wearing a respirator if you have one as it cuts the smell down to nothing (if the smell of guts bothers you)
PS nice job, six in one hunt (I got five and two pardrige on my best day).