The offset difference isn't really significant enough to make a major difference in handling. The thing that won't be in your favor is the wrong-sized wheels (not identical to stock diameter and width, and within 6mm offset) will put you into BSP (B Street Prepared) with a much harder PAX/RTP and much more expensive, fast and difficult to beat cars.
Something else to consider is that those big, wide wheels will significantly increase your rotating, unsprung mass (and even if they don't significantly increase weight, the greater proportion of mass at the rim will increase the inertia of the wheel), making direction changes, acceleration and braking less responsive.
If you want a great set of wheels that (imo) look good and weigh very little, and are also legal for stock class SCCA autocross, check out the Enkei RPF1s. 15-16lb, available in all the right widths, and with offsets close enough that you can get them legal with the allowed spacer. These would also be good wheels for road course use.
That said, don't let autocross classes (or internet forums) define your mods unless winning is your goal. Just do what you like and can afford and have fun at the events.