That is not a small undertaking. I don't think I would do it all at once, and I am not talking about just any "live rock" that you can pick up at the LFS. I swear by real ocean live rock. Check out Tampa Bay Saltwater
https://tbsaltwater.com/ . Do a little reading up on it.
I might add 8 pounds of base rock from the "Treasure Chest" page. Take out some of the old rock, and add in the TBS rock. This will prevent a "re-cycle". See how it goes, Then after a couple months, take out some more of the CaribSea and do 5 pounds of the "premium". YOU WILL GET HITCHHIKERS, both good and bad, but I would never start another tank without real ocean live rock.
Check out my tank thread. I also started saltwater with a 32 biocube. I loved it at first, but eventually tired of the curved corners, mediocre lights, and the closed lid. The lid tended to cause it to overheat in the summer. Maybe not such a big deal in Michigan... I also am not a fan of the "Cube" format. I feel like it tends to stack the fish on top of each other and promotes aggression.
The Gals at TBS are really great to work with. If you start an email dialog with them, and explain your situation and your goals, they will totally work with you and deliver what you need.
If you think you are going slow, then slow down! Let us know which direction you go. Best of luck!