When it comes to the arches, put small cuts all around it and gently bash each section of metal into the arch. If the paint does split, you may want to cover it up in some kind of rust prevention stuff (underbody seal etc)
With regards to bump stops, they look like the yellow thing in the following picture
You bascially stick it on the shock absorber along with the existing stuff, and it prevents the shock from moving as far as before, stopping wheels rubbing on arches etc.
