tadpole For a 75 gallon tank you will need at least 75 pounds of live rock (maybe a little bit less for cycling)
Wet/Dry is a no go, the prefered filter is a refugium or sump. The bioballs well eventually become a nitrate factory so may as well remove them befor you start
Skimmer: get one that is rated for a slightly larger tank. It is always better to over skim than under skim.
Power heads: You will need min of two of these for circulation. There is no best place to put these but I recommend one at either end of the tank and you can move them as required.
As for water I use NSW (natural salt water) but you can mix your own but if you have to go this way then do a complete check on it before adding it, and you will need a supply of ro/di water for topups.
Now just have some fun*celebrate