Highly suggest drilling the tank, hang on overflows an have problems and cause a big water spill on your floor.
As far as your first purchase you need to decide what you want in the tank. What corals? Softies?LPS? SPS? And stock list. This is always the starting point.
Things you will want/need:
Protien Skimmer
Return Pump
Powerheads
Heater/chiller depending on location
Live/Dry rock/sand
Also you may want to look into an Ro/Di unit, i highly suggest using it.
A good skimmer and good flow should be your main focus along with lighting for a reef tank. Skimmer and flow combined keep nutrients at a minimum allowing corals to thrive. These three things is where i suggest the most amount of money be put into. Your lights will be good for most things except things requiring intense light.
Not sure how much you have to spend.