Welcome to canreef! A RSM130 is a great way to get into the hobby, so I hope you enjoy it!
Sand is a confusing topic to me still. I own a RSM130 and have about 2.5 inches of white sand in there due to the fact that I wanted a sand dwelling anemone as the centre piece. I'm sure others will chime in with their opinions. My opinion on sand is to look at what you want to put in the tank. If something benefits/needs sand, add it. If not, try going without to see if you like it. You can always add it later.
It is a good idea to get a few add on's for the RSM130. Here is a link to someone on canreef selling 3 of them.
http://www.canreef.com/vbulletin/sho...ighlight=steve
Believe me, they will make your experience much better for the RSM130.
I don't know alot about RO units except that I have one. I'll let someone else chime in on that unit if it is good enough or not. I personally feel that a good RO unit is an essential item for a salt water system.