i would upgrade my rims and tire, if the width of the tire is increased, rim offset should also be increased?

Answer 1

Rim offset should never be changed by much - it can really mess up your steering and suspension geometry. The general rule of thumb is no more that 1 to 1 1/2 inch with RWD, and no more than 1/2 to 1 inch with FWD. More than this will make your tyres wear really fast and unevenly, and puts much more strain on your wheel bearings - especially on the rear. Just make sure they don't rub on the fenders or the suspension.

You could go for more offset, but it means complete custom fabrication of your suspension to make it work properly - pretty expensive stuff!