Well I am gonna go out on a limb here and say I do not necessarily agree with the have the tank before you buy the fish or rehome the fish thing, especially if the fish is only 1 inch long or so when you get it. Even more so if you are a person who follows through with your intentions when you pick up the little fish.
True many people will pick up fish without forethought or foresight in what they are doing. Yet, personally in my journey in the hobby I have taken on fish knowing full well that they will get big and also not knowing the full species profile(to that end not all fish fit their profile as they have personality quirks that defy the profile).
This being said there are times where the chance to get a fish comes along and you do not have the end tank set up ready for them, but they will not be needing that for months or even a few years so why pass up on picking up the fish because of what will be needed in a that time frame. As I say this I can see the responses from some that might come, but I am one that believes in bigger is better tanks and like to make sure that I am able to place fish in such a place for final environment. Though I will say I think that pacu and certain types of catfish should not be for sale in the hobby as essentially they are a food fish being farm raised for that reason and should not be in the hobby because of how big they get.
Hope your trigger makes it to a nice size for you would like to see pics.