Hi Deevad, there isn't a second docked, but it would be cool
, I use a No-Title Slim Gtk 2.4 theme.
And to get the preview I split the view first vertical and then horizontal, arrange the split lines and move the brush window over the not needed third view,
it's a little bit troublesome, but it gets the job done.
That's a grate idea with the palette window, just add a preview window with the same functionality as the palette, so you could paint in it zoom and so on like a regular canvas, no UI complications.
For the thumbs I just use Shutter 0.87.2 print-screening a selection.