Acrylic is an especially good choice for beginners. It's cheap and easy to shape, so it's not a huge investment in time and money if you wreck a couple. A broken scale can often be recycled as spacers, so it's not always a total loss.

As for polishing, I generally hand sand acrylic to 1000 or maybe 1200 (depending on my threshold of boredom that day), then take it to the buffer. Caswell sells a plastic-polishing compound that works wonders. I use a 6" sewn wheel for this. The keys here are to sand out any deep scratches, then buff the entire surface from several different orientations. It may take a couple of sand/buff cycles to get your desired result.