This is what I was thinking of for the plan above.
1. Remove 45 lbs of rock and coral from LA, put into 55g. I would leave the rock I added from my 55g to make sure I kept some bacteria
2. Move fish from 55g to 125g (with my Blue Hippo and Clown) to treat for ich
3. Test water levels daily and perform water changes if needed (since a lot of bacteria will be killed by the treatment).
4. After treatment, leave the fish in there (as this would be a Fish-Only tank, so if ich ever seemed to get into the system, it is possible that I could treat in the tank), and probably add some dry base rock
5. Make 55g a full blown coral reef tank with inverts, but probably no fish (unless there are any that are not able to acquire ich).
Thanks for reading this! Nothing is set in stone yet, just some ideas.