125Gal start up Need some addvice

Hey just wondering if any of you can help me out I am going to be starting up my 125gal tank, I don't have it drilled so wondering what I need to make this system work well for corals I am not sure what corals i am going to be getting into but want to make this right the first time and not have to spend TONS to upgrade so kinda wanting to do this right the first time sorta speak, lol I know I will have to upgrade a few things but just want to know what i need to start say basic and then add on later type deal. Right now I have the tank stand 2 aqua clear 500's and the heaters so not much any help would be great thank you so much.

Jenn