Rebbetzin Heller notes that Haman’s imagining these actions seems childish. In actuality, having wealth and honor already, the idea of being king for a day is the only thing Haman lacked.
The Ben Ish Chai points out that the letters that spell the word melech (“king”) could be an acronym for merkava (“transportation”), levush (“clothing”), and chroz (“proclamation”). In other words, the three things Haman suggests all represent the essential elements of royalty.
From the exact opposite perspective, R’ Elisha Gallico adds that Haman was thinking that, just in case these honors were not meant for him, they are still non-substantial and without any actual permanent position change. Throughout his advice, then, Haman can be seen as asking for the greatest honor for himself, with the backup plan of this being meaningless if it is meant for someone else.
