Well it depends on what you plan to keep in the tank.
If you plan on a having live rock and fish ONLY... then I would suggest some sort of wet/dry system to hang on the back on the tank, maybe a skimmer altho it's not necessary. I would also suggest you invest in 1-2 pretty strong powerheads. Water movement is extremely important in this hobby. Lighting won't really be TOO much of an issue as the fish will do fine with standard lighting.. however the live rock may need a bit more lighting than can be provided by "stock lighting". Others may have a better answer for you on this one.
Everything is different for a reef tank however, because it will house corals and far less fish than a fish-only. The lighting needs to be upgraded, the filtration needs to be upgraded (maybe you'll want to stick with just LR and LS for filtration and a skimmer), the water movement via powerheads really needs to be upgraded for this tank.
So I guess the next question before I spend 10 minutes responding is... how much cash are you willing to spend right now to set up this tank properly?
No matter how DIY you get or how cheap you get some products.. it's STILL going to cost more than you anticipated so be forewarned
But it's more than worth it!!
Also... I would ditch the undergravel filter personally. Those work great for freshwater tanks, but not for saltwater IMO.
This is all my opinion on what's worked for me so far so take it with a grain of salt
ps- reef tanks are awesome! fish-only are cool.. but there's almost nothing more rewarding than a healthy tank full of coral
