I have a 3 to 4in sand bed. It also depends on what you want to put into your tank, some animals need a deep sand bed, while some don't need a sand bed.
My sleeper goby loves his sand bed, as it's deep and has life all throughout it. I see little bug like creatures come out at night and scurry around my tank. I don't know what they are, but I assume they are helpful. Most things that come with your live rock or sand is helpful.
I bought live sand and live rock. To me spending around $37 dollars each for 3 bags of 20 pound CaribSea Fiji pink live sand was worth it, but that is when I set up my 29 gallon tank. When I switched over, I bought 30 more pounds of Topfin normal sand.
If I where you, I would go ahead and buy the majority of your sand normal. I would only buy maybe 2 bags of live and throw that on top of your other sand. This is cheaper and will help get the other sand live faster than just the live rock alone.
As for the how deep your sand bed is, I was told that a nice deep sand bed helps a lot. From my experience it has not disappointing me to have a 3 to 4in sand bed. I just don't know if that would be considered deep.
Fish Sticks, the best thing you can do with your dead fish.