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
? And stock list. This is always the starting point.
Things you will want/need:
Heater/chiller depending on location
Also you may want to look into an Ro
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.