Sandpaper should be able to get in most of the hardware shop, I think.

if you have the budget, considering the essentials from meguiar's (user/beginner friendly, albeit more expensive though)

for methods, do a search on this thread or look up meguiars' site for video guides or even youtube videos
normal wash would do, they are generally rubber based paint anyways, so whatever that treats/deal with rubber good should be applicable.

I don't think there are even milder shampoo than car shampoo that is still effective to clean

Perhaps you can try human body shampoo if you're that ocd

I'd rather you not do anything than bear responsibility on your mishaps