I think the mount will work on most surfaces. Best one I found was at Walmart and called schoch or some such name. The clamps open wide to accommodate the s3 in a protective case.
As far as landscape mode goes use Google Play to look at reviews. Reviews on the Amazon app store seem to be few and far between. Look at launchers such as Golauncher, Apex, Nova, ADW, etc I think they all have the ability to make the home screens landscape.
I personally use Golauncher and love it but others will suggest Nova or Apex. They do have a bit of a learning curve but once you get past it the things the launchers can do are awesome.
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