Welcome.
I enjoyed reading your story. I also took quite a while to figure out which hybrid to purchase. I think you will enjoy the HCH-II.
You say your partner got a free 90's Buick Century? If it's anything like my 90's Oldsmobile Ciera, its sister car, it should be capable of getting some pretty good highway mpg's. Not as good as the HCH, though! (And in city driving, you will beat your partner's car, hands down.)
Definitely take the Honda in so they can take care of that alignment problem.
Best of luck to you with your new car.
As for tips, I see you found Tarabell's article, so that will come in very handy I'm sure.
Basically I stay at the speed limit, leave plenty of room between myself and the car I'm following, and keep an eye on my tire pressures so they don't get too low.

If you're not part of the solution, you're part of the precipitate.