Get the 2.5L 4 cyl... it's the Mazda MZR engine. This engine has been proven to be nearly trouble-free given minimal care and feeding, and in general provides stellar UOAs and engine life. Mine went as far as 17.2k on PUP, but I would probably dial things back to the 13-15k range (or just OLM @ ~10k if she's not mechanically inclined). In 115k of ownership, it needed a grand total of: 2 sets of rear pads and rotors. That's it. I went ahead and changed the thermostat @ 100k just because, but it didn't fail. I did do a couple D&Fs on the 6F35 with Amsoil ATL, and obviously oil & filter changes. I used the XG3600 size, which comes right against the belly pan. 3614 is the "normal" size.
One thing of note, especially if she's up there with you for Mitten winters... she'll need a GOOD set of snows, I'd recommend Blizzaks. I had a highly rated set of all-weathers on mine, and even the first winter with less than 6k on the tires, I was less than smitten with how the car reacted. Other than that, and as proven by some of the other members here on the board, the 2009-2012 Fusion with the 2.5 is most definitely a 300k-capable vehicle with just basic care. Just remember the mantra for the 6F35- change the fluid early and often, and make sure to force the shift logic to reset after each fluid exchange. I wouldn't use a flush machine, just drop the belly pan the first time, and mark the belly pan where the trans drain plug is. I punched a 1" hole in mine with a paddle bit so I could remove the plug without ever removing the belly pan again.