Well it helps to know what you want in the tank because that lets you know what you need regarding water flow,lighting,etc.. I imagine you're shooting for a mixed reef, which is a tank with exactly what the name implies mixed corals (lps,sps,softies,mushrooms,etc..). Yes you can mix hard and soft you just have to be careful where you place them in your tank and use different things such as chemical filtration,protein skimming to help.
Since you plan on drilling the tank you have alot of flexibility regarding flow and water movement in your tank. In a reef tank you want to achieve some type of random water movement.
Go to this website and look at the different kinds of corals you like
Corals
Have you bought any equipment yet?
I would suggest you buy a good book on saltwater aquariums, and read as much as you can on forums like these (use the search option)