Welcome to TFF!

Hex tanks, being taller, are best for taller fish, such as angels. You will want to remove the crushed coral, this will raise your pH, a situation you don't want to start with. I would save it for future use; you may keep fish in the future that do better in a higher pH. Remove & save the coral for this reason as well.
With heater you want about 5 watts per gallon. A 250-watt will work in a warmer area; go with a 300-watt if you keep your house a little cooler. Don't skimp on heaters, it's false economy. Visi-Therm or Jager heaters are some of the better ones in the US.
Aqua clear makes one of the best power filters, I have around a dozen running. An AC 70 would fit in well with this tank.
Discus are not a fish you want to begin with, just like you don't want to start out with driver's ed when you are a kid with a pro stock car. You will want to work your way up to discus after some experience. It is something to work towards, as discus are beautiful fish.
Being a tall tank it has less surface area, which means you will have to stock lighter than a tank of more standard dimensions. Check out the pinned articles in the beginners section here, especially the ones on cycling.
Enjoy the tank, hex tanks are real lookers!
