yes
Not sure its as easy as that, but yes, you keep roughly the same offset as wheels get bigger. Tehnically the offset should get larger numbers to compensate I think. Any good wheel vendor should be able to help with it. The main thing is to start of with the width and offset of a wheel you like and work it from there to make the ones you want to match
Depends if you want wheels that = win or wheels that = fail
+12 on a 10.5" wheel is perfect fitment (Awaits Docwra to say that anything above 0 is a failiure )
Yes its all personal preference, hence why I suggest finding someone with wheels you like the look of (fit wise), find the width and offset and them make sure whichever you get they have the same relative offset I'm sure though to keep the wheels the same "flushness" to the arch, as the wheel gets wider you generally need a larger offset to keep them in the same place
Stew.. what are the offsets etc of your wheels
yes i know they are 20's