It depends, what are your goals for the tank? If it is a FOWLR, then that is probably enough, especially if you're going to add some fish that need lots of swimming room (it looks really nice, by the way). If it's going to be a reef tank, you could add some more as you will need room to add all the corals, etc. especially if you have some that sting. 1.5-2 lbs of live rock (depending on size, shape and placement of the rock) will generally give the tank a pretty full appearance.
How old is the tank and what's in it? If you add live rock that hasn't been well cured, you may start a mini-cycle if there is a bunch of dead/dying stuff on it. Also, for what it's worth, if the tank is new and has no critters in it, save yourself some headaches down the road and put in a DSB now. If you try and switch later, after you have a bunch of fish, inverts, etc, it will be a major pain in the rear (I know this from personal experience!).
HTH