Troy James gave you great info. Basically filtration is secondary in SW and serves mostly just for circulation. The live rock/live sand is your main biofilter, which is why you can almost instantly cycle your tank by adding them. To be safe you should continue to still stock your tank slowly until youre sure its safe.
My tank is about a month old and it is lightly stocked but I never had to deal with ammonia or nitrite spikes like in freshwater. The main difference Ive found is the cost. The live rock and sand is probably going to be your biggest expense when setting up a new tank. Ideally you want a pound of each per gallon. Im tight on money so Im adding my live rock slowly. If you have the money you could add it all at once.