Hi all!

One of my friends does game programming, but is not all that impressive in the art department. I happen to be able to draw, but up until now I've never done sprites for games, and as it turns out it's quite a bit harder than I had expected.
Not wanting to let the team down, I went on the internet and found a few tutorials and such on how to draw pixel art. I decided that an isometric view would be best suited to my drawing style, and have been trying to get my mind into it.

So far I've only done one character (the rest being cubes, pyramids, spheres and other basic shapes for practising purposes), and I was hoping to get some input on it.
I started with a drawn image (by the way, if anyone has any tips on how to draw isometrically that would be appreciated), scanned it in, and then went over it pixel by pixel to make my little character here:



Meet Alex. I've drawn this character many a time before, and I think that fact made it easier, but never as an isometric sprite. There are a few things I would like to know:
Currently, Alex is just big enough to have enough detail. Should I try making the sprite bigger, or does pixel art become exponentially harder the larger the image?
How would I make the grass look more like grass? Referring to the middle bit; the edges are the only part that imply that it's grass.
Are the colours I've chosen suitable?
Does the sprite look like it is isometric?
And yeah, anything else you can find wrong.

Greatly appreciated!