Your offset requirements are determined by your suspension and where the manufacturer placed the hubs. (and to some extent, how they engineered the bearings to deal with the stresses put on them) So, the question is: What offset are your factory wheels?

It's perfectly okay to deviate from that by 5, maybe 10mm. Moving the tire outward (less negative offset), is preferred to get a wider track. I think the net effect is a reduction in body roll due to changing the geometry. (my brain hurts when I try to comprehend why)

If you deviate too far from the factory offset, you can cause premature wheel bearing wear.

Bottom line: Most FWD cars come with an offset somewhere between -40 and -50. Most FWD aftermarket wheels come in offsets of -35 to -42, any of which will work just fine.

If you're getting wheels that are strictly for autocross competition use, then you might want a more extreme offset. Why? Because they're going to be much wider than your street wheels, and if you don't change the offset, they'll scrub your struts, inner fenders, control arms, etc. For instance... if you wanted ultimate performance, you might fit a set of 13x8's... with an offset of -20 or so.