The arches are mounted via 5 or 6 bolts thru the wing panel. The bolt is actually a short thread that is attatched to a small right angle braket which is fibreglassed into the sportspack moulding.
1 notch will need to be filed out to clear the bottom door hinge.
As for the panel cut out, that all depends on the wheels / height your car is running. You would aim to remove about 25mm from the front half of the wheel arch (same arc) and then continue to blend it into the original arch line from the very top to the seam.
If you want it to be a low car, you will need to mount the front arches on a slightly different angle (pitch the front up a bit) to clear the tyres when turning. It's that, or cut a bit off the arch
The choice is yours.
I have seen some special Sportspacks made of very flexable material kinda like rubber compuond that is paintable - they would be alot easier to work with and could survive a few decent knocks too. Theyre about 80 dollars more for the set though.
Im sure there are pictures on Ausmini somewhere, do a search for "sportspack arches" and see...