Easy and Normal difficulties are both, well...easy.
The difficulty definitely comes from lack of information given to the player. Ideally, this gets fixed during Story mode, where we are slowly introduced to objectives over time and given express instructions on where to go and what to grab.
But as you've already said, there are videos on youtube regarding this for Arcade mode. As long as you know how to actually complete objectives, Easy and Normal Arcade should be pretty easy. You can generally do two objectives at a time on Easy (you can reset Chiku's timer from the computer room on Easy).
Normal, you should definitely only do one objective at a time, run back and reset the girls between each (must go to the Kitchen on Normal or Hard for Chiku). You can probably get away with two if you purchased a helper and use it to make a distraction. While I haven't done extensive testing, I feel like when the power goes out, it slows down the girls' countdown a bit. I need to test that some more.
Hard, I wouldn't even go near, though. Definitely requires knowledge and proper movement, along with helpers, to fully complete. Not really worth doing except for your own satisfaction. Or do what Jermain said and just get easy money to buy yourself some boosts if you're still struggling with lower difficulties.
This all being said...really wish the dang auto-run wouldn't get stuck. That's my main complaint lol.