In last version there is no option to pick colors form the image. But you can load/save/edit/create palettes until 192 colors. And no for transparency.
I ended up purchasing a copy of this tool by the way.
To clarify: what I meant by the first question is, is there a limit to the size of the image you can put in the tool? like if I put a very, very large image in this tool will it have problems?