1 1/2" is the easiest but is not considered a beneficial filter. 3"+ is considered a deep sand bed. If you are just starting out, plan on 1 1/2" for looks and get the best skimmer you can afford.
I only use Aragonite. It's been my favorite and trouble free. You can buy a couple of 40lb dry bags and add a few pieces of live rock or a couple of cups of sand from an established tank to seed it. Within 2 weeks it will all be "live". A note for our Eastern folks. A rumor is that you can buy Southdown in Hdepots. If so that is an excellent substrate. It is a calcium knwon as Sugarfine in the trade. It will break down and leech valuable minerals into the tank like aragonite does.