What bits need drilling out please to remove the wheel plastic housing? The inner housing is bolted on the body/wings, there are only 2 or 3 clips and those you can just pull out and even re-use.... You'll have a lot of rotten leafs etc back there, always worth clearing out!
Rusted arches are not an MOT fail, unless the bottom end is through (but at that stage your sills will be as well)...