DON'T CLOSE!!!
I agree with what others have said about holding out through the holidays if you can afford to. Beyond that I would still stay open :)
I have a few suggestions that might help...
1. You have a lovely, heart warming story about your possum which I would include in your profile and how it has inspired your art. As well, keep the links to other sites but I would put them right to the very end - you want buyers to stay in your shop as opposed to clicking out into the wide world of the internet to maybe never return. The other option here is to perhaps (if you can afford again) is to donate a percentage of your profits to a possum based charity. Then that information could actually be in your listings as well - you could make this a reciprocal relationship with the charity too.
2. You're pictures... There is a big thing here on Etsy about white backgrounds - as boring as it is. With your miniatures some of them are on white (the polar bear) which look good but the others are outside which is cute and maybe good for pic #2 but I would change the first shot to a white background. This would help treasury makers. I've seen loads of miniatures on the FP and there is no reason yours can't be there too!
3. Art... I would work on 'staging' your artwork.. The pictures you have are lovely (especially the close ups which are really cool) but when you get to the picture with the frame it's a bit unwhelming. Personally I would never put a black image into a brown frame - that's me. As well, I find that frame really heavy. But beyond that I would put the art in a frame (or not depending on the artwork) but then place it on a mantlepiece with some flowers, a coffee cup, even one of your miniatures. Basically something to show what the pieces would look like in a buyers house and a more 'clickable' or 'treasury-able' photo.
Beyond that I think your titles and tags are really good. The thing I've realized about the magic 100 is that it's not magic and I think it really works if all you are selling in 1 thing. 100 hats is fabulous, 20 hats/20mittens etc that adds to 100 is slightly different.
Don't get disheartened by people who dislike possums. Everyone is different with different experiences. I love german shepards - other people wont let them in the house. I have 3 cats and people are scared on them - even though they are the most gentle animals ever.
Keep going and do what you love. When you stop loving it then it is time to stop - not when the sales are down.
Good luck. I apologize this is soo long and probably full of spelling mistakes too :)