The maximum sensible size is 15", given that is the biggest wheel fitted by the manufacturer on the 100hp.
Think it will just look wrong if you go for 16s, plus the ride will be more compromised. With that amount of grip (guessing you will get decent tyres) you ought to be able to drive flat out everywhere with a 1.2. It will be no fun handling wise but if it's just looks you are after and you aren't into hammering it into corners then you'll be okay I guess.