The cutting has been done so may as well just leave the FMIC in there and seems like it is a decent fit. The intake situation would see worthwhile gains in drive-ability and some power.
With rims 18's can look a bit too big depending on the style. 17's look killer
2011-2014 WRX
Size: 17x8"
Offset: +53
Bolt pattern: 5x100
Weight: 9.5KG
2001-2004 WRX
Size: 17x7"
Offset: +55
Bolt pattern: 5x100
Wheel Weight: 8.5KG
STi version 7
Size: 17x7.5"
Offset: +53
Bolt pattern: 5x100
Wheel Weight: 7.7KG