Evening
Good call on the gulf rock. Like mentioned leave the rock as is. Some plants may die off, some may get eaten by fish you put in, some you may end up liking and let growi or end up pruning and removing.
As far as ammonia, I would grab and ammonia alert badge and prime for an emergency. I would also have some rodi and salt ready, but I doubt you will have any issues. If you got your rock from one of the reputable vendors the rock should have little to no die off. I just set up a 75 using rock that came out of the ocean 2 days earlier. I put fish and coral in the tank right away and no issues. It Just takes planning and monitoring.
On the down side, you will need to monitor for hitchhikers for a while. The worst is usually gorilla crabs followed by whelks. Since you put the rock in the tank you may want to hold off on permanent rock scape in case you need to pull it apart to get a crab out.
Not sure about what is on the snail or the rock. Did not see if you have fish in, but I would get som in there if not.
You could do a build thread for a badge and so we can follow if you like