Tire height + lots of questions

Hi,
Here is my situation. Im a broke university student, just got a flat tire and have no money what so ever for new tires or a new tire( to be honest all my tires are pretty much bald). Before the flat i was running yokohoma 245/50/16 on all four corners. Same situation now but with a spare :(
Now ive been looking in the local used adds and found a bunch of tires but i dont know if they would fit. I am willing to switch things around too, just to save money. My front tires are still good for a little while so i could put the front ones out back and get 2 skinnier tires up front or keep the front ones and go a little wider and taller out back. Im running your regular 16x7 pony rims.

will a 225/60/16 fit up front with 245/50/16 out back?
will a 255/65/16 fit out back with a 245/50/16 up fron?
will a 205/50/16 fit on my pony rim or is it too skinny?

What are my options guys?
How big and tall can i go out back? ( i dont care about the speedo reading or minor rubbing issues its only for 2 months)
How skinny of a tire can i put up front on my pony wheels and how tall does it have to be to match the back ones (i dont care if the back is higher then the front, i just dont want the other way around)

What im asking is....what are my options here for tires any suggestions would be appreciated!!

Thanks


Simon