oh what the heck? you just stole what i was writing!
and to answer your questions :
1: Kittens and cats will Hunt down vermin and kill them , which can rot away and cause half your dwarf population to go Mad and start punching everyone , set up a refuse pile so that dwarfs will dump that pest away without miasma and Insane Dwarves , word of advise : kittens and cats will force dwarfs to adapt them , and if they die , said dwarf will be a inch away from snapping , and if the thinest thing goes wrong for them , they are going mental
2: just dump your junk outside , really , those kobolds will just steal about whatever carp they can lay their hands on , Goblin theives are a different story : they steal your fortress children , causing said kid's father(or mother) to go mental , and thus dumping junk about won't work , do what minty said : place and restrant animals(not pets , since whoever own said pet will go insane if they die) at your gates.
oh , and word of advise : don't dig randomly or you will uncover something Precious that could turn your fortress from a extreme guarded fortress into ashes due to goblin sieges(also , this references to the FUN you can get)
and yes , i am a DF Veteran