Well, I got done with the AC. It was unsatisfying (my windows never resemble the ones air conditioner designers target), but I feel the installation is safe. I hope these BTUs are worth it.
Re: AC support brackets: The weight rating isn't all you should consider when picking one. I have a 50 lb. AC, so I got the small one that can support up to 80 lbs. I installed it, and it was too short to reach the actual wall; it braced against the outside window frame, which is was not comfortable with. So, I had to return it.
This, hopefully, concludes National Backup Fixing and Air Conditioner Installation Day.