Wheels...

[Yonzie]

I have been confused for a while on which wheels will be able to fit the AE86...
Currently on my car, there's 205/50-15 rubber on 15" wheels (unknown width). They aren't that nice anymore (although I like the looks), and I'm thinking of replacing them in the future.
I have heard that the original wheels are ET (offset) 21...
The proprietor of my local aftermarket car parts shop says that it has different offsets for front and rear (this is corrobotated by other people on the web), but he wasn't sure what they were exactly.

So, how large wheels (max diameter, max width) can one fit on the '86, and what should the offset be?
I am perfectly aware that 15" gives the best handling, but I would still like to know what the limits are in each direction (I'm curious) ;-)