Live rock is the simplest option, it just sits in the tank and does a lot of the work for you (as far biological filtration goes). Without live rock it can be harder to maintain a stable tank and you'll need more equipment without it. Plus live rock makes the tank interesting and makes most fish more comfortable in the tank.
Not having corals makes things easier, you can use whatever lighting you want and you don't have to watch calcium levels etc as closely. In my opinion the keys to a good marine tank are live rock (biological filtration, looks good, home for fish, also provides food in a way), good water movement through-out the tank (stops detritus from settling, can prevent algae, aerates the water) and stable water parameters (salinity, alkalinity, ph, nitrate etc). Of course there are a lot of elements, such as skimmers etc, but those are the basics and most important. Get those three things right and keeping marine fish can be pretty simple really, just my opinion anyway.
