Its nicely put together, just a couple of comments.
First, try to remove the nubs, it improves on the look. Right now its pretty noticeable its been cut out of a runner.
You don't need to use sandpaper, especially not if the parts have a special finish.
Second, regarding the panel lining: http://gundameisters.blogspot.com/2011/03/gunpla-tutorial-panel-lining.html