Beginner kind of jumping into this, 3x A4+ from Innosilicon with some questions.

I guess I'll start with the facts, electricity costs .07, running this in an apartment, located in Florida, 3x A4+ LTCMaster units.
I just have a few base questions.

1. Location wise because I'm in Florida, do I need to be worried about humidity from the ducts with the outflow going outside?
2. What are some essential things I should buy now that I might regret not buying later?
3. Would it make a difference if I run a duct directly into the AC vent rather than just having the units run in the middle of the room?
4. On a scale of 1-10 how important is putting a lot of research into the best pool vs return?
5. My cousin wants to live with these units in his bedroom, is he going to go insane and regret this?

Any extra advice that comes to mind from reading my questions is also well appreciated.
Thanks guys!