I have time to chime in, after reading the whole thread. 5 gallon tanks are the most alluring and yet the most annoying, because the offer so little.
No to whiteclouds, pencilfish, gouramis ( be it sparkling or honey), and no to almost anything, sadly. Scarlet badis are not recommended for beginners because they need live food and they make such a mess when eating, like pea puffers, they almost always result in overfeeding, algae, issues with the tank
If you were to go the road of any shoalers, it would have to be the smallest of rasboras like the least one, and even so, group of 8 max and shrimp and keep rigorous water changing schedule, which would be harder to maintain.
As for Hara jerdoni, people here keep a trio in a 5 gallon, have it breeding, no problem, but you wont see the fish. This would result in the tank looking empty and you wanting to add something else to them. I would advise against it. Believe me, I know, I have a 5 gallon with bottom dwelling invisible fish and I have to bite my hand all the time to not add fish in.
While I have my clown killifish in a slightly larger tank, based on their interaction I would not see a problem keeping a trio of them in a five gallon, one male, two females. They are hardy, active, near the top so always visible, colorful and can handle the move ( i got mine shipped via post, they are hardy). Paired with a nice snail they could be a good tank choice for a five gallon
Regarding the thai microcrabs, you would have better luck with shrimp, every keeper reports they never see their crabs once added to a tank to their liking.
Have fun setting up, you have time to pick up the fish. Ofcourse betta is the obvious choice, given they live only one to three years, depending on their genetic setup and your feeding, and would solve the question of what to do with the fish once you finish school. There are some stunning koi ones avalable now and some of the fish have puppy like personalities. Some are assholes though ...