Matt,
I've fitted 17s to my EP91, I've konis with Fensport lowering springs!!
And yes I did roll my arches, I suggest the best course of action is to get your arches cut back and welded since it is going to the bodyshop anyway!!
Tyres are really important as well. Not sure where you go but AP Tyres are really good. I changed my rear tyres last week and got some Falcons, they have a sloping tyre wall!! So mine don't catch at all now!!!
Hope this helps
Nath