A 3-4" deep sand bed and 1.25lbs to 1.75lbs of live rock per gallon is excellent filtration for your fish. A 55 gallon tank would take roughly 70-90lbs of live rock. To save money, you could buy 2/3 of the cheaper base rock, and 1/3 live rock. The base rock will eventually become live rock, and will still serve as filtration media in the mean time. 2-3 watts of light per gallon will keep your live rock healthy. A 55 gallon tank with live rock would need at least 100 watts of light but 150 watts would be better.
When you add new live rock, you'll need to wait 4-6 weeks for the tank to cycle. Fish and critters can only be added after cycling. You'll need test kits to ensure that your tank is cycled.
Once the tank is cycled, you'll want to add a clean up crew. This consists of worms, stars, cucumbers, etc that sift through the sand and clean up waste and algae.
You'll also want your tank's water to turn over 10 times per hour. Sump pumps, power heads, and skimmer pumps turn the water.
Before you start buying equipment, do your homework first. Read through the posts here, and do word searches for specific things that you want to learn about. You'll need alot of equipment, and alot of knowledge to successfully keep a marine tank. Maybe you'll want a refugium or maybe not. Maybe you'll want one big pump, or a few smaller ones.
