I like these... there very cute.

What you said about tiling though... well tiles can do wonders. If you make 3 or 4 seperate grass tiles NO ONE will be able to see "the grid" especially at this size. Plus, if you ever want to expand this little scene anymore you can do it easy as pie. Tiles are a wonderful thing.

the duck is actually pretty good, though I think if you shorten her leg it might make her look less like a chicken. Ducks have shorter, flatter fatter feet then chickens
One thing I noticed that seems off with the whole piece is the shadows. Your lighting appears to be coming from the upper righthand corner on most of your objects, but the shadows fall direcly below, like the light is overhead. They should be going to the lower left.
A few other minor citiques I have are
-the tree could be a little pointier, but that might just be a style thing and reads fine the way it is
-I like the pallete you have though it could use a little more contrast exspecialy with the greens and browns (don't worry, I have MAJOR problems with contrast too.) and the water could use another color
-The shadows under the butterflies seem off more than the other shadows. Maybe there to far away from the butterflies?
Anyway, good luck! It would be really cute to see this animated. love the little lost duckling!

P.S. I almost forgot! For help with the 3/4 rpg perspective the tutorial by Cyangmou on this page
http://www.wayofthepixel.net/pixelation/index.php?topic=14148.0 might help