Hi,
Every single tank is as unique as the person who sets it up, no two are exactly the same. You have to do what works for you. Do you have the energy to clean your old sand (it's quite the chore), since you like the Fiji pink do you even want it? When you ask advice sometimes you need a goal and ask about exicuting your plan.... LOL...if ten people answer you, you will get ten different opinions.
Your only real concern is to make sure your fish have enough good bacteria already established in the tank so you don't have an ammonia spike and start a cycle. You can accomplish that in many ways but it is the most important thing when upgrading your tank. As I remember your other thread....all the "different confusing" advice had that one goal in mind. So choose a method and commit to it....and enjoy that larger tank, a 75g is a great size, much better than a 55g.