3.0 Manual RWD before you ask.
There should be no extra wear on anything running these, as you are not messing with anything suspension by putting on tires.
As for MPG, bigger tires tend to lower that number, but for me it is liveable. I went from using roughly 47% of a tank to 52% when going to a spot about 2.5 hours away. But that is also keeping the speedo at 75ish MPH (bigger tires and non calibrated speedo means I'm going a *bit* over 75) So I'm also burning it faster to drive faster.
That brings another point, the 31s will mess with your speedo. And it won't be always X number off, it is an exponential equation opposed to a linear one so the faster you go the more it will be off. You can fix this by paying someone to recalibrate it (dealer?) Or by getting a program or software to do so yourself (I plan on using Forscan).
As for towing, I have not had any issues doing any heavy duty towing. Pic below shows the most recent thing I towed (which is like 2 or 3 times what I am "supposed" to tow according to Ford) and the tires did not hinder me in any way. These tires are heavier than stock size too which means they are more effort to stop, so with stock drum brakes towing this may have made it a pain to stop but while not towing there is no huge difference.
Edit: when spending good money to buy new tires it will be worth it to get an alignment as it sounds like one is needed.