To your last question: The founding fathers predicted that eventually some rich guy would decide not to take the presidential salary, and then after him it would become obligatory for all presidents to waive the salary, making it more difficult for anyone who wasn't already wealthy to get the job. George Washington, the second wealthiest president after Trump, tried to not take the salary but they made him anyways.

So maybe Trump is going to donate the salary to charity idk. You can say you don't care about the expenses because of scale, regardless of what it symbolically means. But you can't then say waiving the salary matters when it's clearly just a small symbolic gesture he can't actually fulfill, he's spending way more than he's symbolically waiving, and his businesses are making way more money because of his travel choices (this seems screamingly obvious but to be fair I don't have the numbers for a fact) than the salary he's waiving. And if you're thinking maybe most of that goes to his workers just remember how the man lives, how proudly greedy he is. He's not particularly interested in spreading that wealth outside his family. (Obligatory "?" because rules. I think I'm breaking the question rule for a good enough reason here, sharing a relevant historical factual anecdote.)