Most feel live sand is a waste of money (Me too) Use the cash to buy a nice piece of live rock instead, you dont need a lot to seed the tank 2-3 lbs will do. You can then use base rock to fill out your aqua-scape, the rock and sand will become 'live' in a few weeks The grain size will be based on your flow more flow = larger grains as it will help keep down the sandstorms.
A lot of your questions can be answered here Articles
Most people create their own problems by not following the basics and refusing to stock appropriate to their system. Gregcoyote 2013
SPS = Stability Promotes Success