If you've got the space, you'll find that you can get a real upright for free in most cities in the world. Sure, it won't be the best instrument ever, but if you ask around you'll find someone chucking one out.
Yes. We were told that we should move our piano away from the outside wall next to a window because the temperature and moisture fluctuations were causing it to go out of tune.
We're in an old house and there isn't a piano-sized space in our living room that doesn't have a window, door, or HVAC intake/vent.
That's a very important point, tunings will rapidly exceed the value of any 'cheap' piano. And typically the cheaper they are the worse they will keep tune, though there are exceptions to that rule.
I can recommend Entropy Tuner, which is a great piece of software to help you tune a piano properly.
