The reason why Peach never hires guards to protect herself is because of her being both too nice to people (outside of Smash Bros and other rare cases ofcourse) and
The reason Mario always risks his live to save Peach is because she rewards him by not making him pay taxes (either that or cutting a lot off them), the cake and the kiss are just a small bonus.
The vast majority of the normal Toads are really poor and the live in those really small mushroom houses because they can't afford better, and only a few of them can manage to live in better status, like in the large metropoli-like cities we sometime see in Mario Kart and such; some Toads which are richer than the mass are those living in the castle, the Toad Brigade, the Toad guards/soldiers and any other wealthy Toad.
The reason why Bowser and his minions can partake sportive events and be incrdibly close to Peach is because Peach is, again, too naive and nice to not allow Bowser to partecipate. She'd feel bad for him, even if that'd make her super easy to snatch and take away to his castle.
The Koopalings are all adoptive children of Bowser, he gave them a home but he was never a true father figure to them; he trained them to use a magic wand and now he uses them as elité members of army.
King Goomba is depressed due to how mistreated Goombas are and he sometimes cries when nobody can see him because of all the mocking his kind recieves, but to appear stronger he always tries not to get sad and/or cry when he gets defeated to avoid making Goombas also get the attribute of being crybabyes.
Wario and Waluigi are distant cousins and they originally weren't called Wario and Waluigi, nor they dressed up like they usually do (with overrals and stuff).
The reason they look like caricatures of Mario is because Wario noticed he was the only other not-slim human in the Mushroom Kingdom outside of Mario and so he decided to mock him by dressing like him and changin his name to mimick his; Waluigi decided to join himand he started to mock Luigi.
Luigi is a bi-curios guy who is into females but he occasionally might get a crush on a male if they're enough pretty or wealthy, like in the case of Prince Peasly; he was also confused by his sexuality at first and he sometimescross-dressed in private asa teen, as rare times he still does it nowdays when nobody's watching (he thinks Mario is unaware of this but he actually knows everything and is completely cool with it).
Even if Bowser is quite rich, but he only spends money when it comes to stuff that he could use to defeat Mario (reason why he has that unnecessairly pimped car) or to expand his empire; so Bowser Jr. thinks he's a beach cheapie because he rarely buys him presents outside of robot-building tools to create robots to defeat Mario but he's cool with it because he finds building all that stuff to be fun. Albeit he'd like if his fater gifted him some actual, non-Mario-defeating presents every once in a while...
He also sometimes wonder who his mother his as he never met her, however after the events of Sunshine he kinda stopped caring about it and accepted that he might never actually encounter her.