18" wheels will fit, it's the width and offset you need to be mindful of.
The Handling Package wheels should be 18 x 8 +55.
For comparison I run 8" +46 and have no issues. If the new wheels are around that you should be fine.
2012 Yellow Blaze Focus SE Sedan (DD+Project)
1992 Bright White Grand Prix SE Sedan (Project)
SR #74/SMk3C #17/YBOC #03