1)I really haven't downloaded any custom food, so I can't help you there, sorry
2)You could have a hack creating a conflict somewhere. The hack conflict utility found
here is a good place to start.
3) There are four things I use when posing sims: moveobjects on, boolprop snapobjectstogrid false, boolprop allow45degreeangleofrotation true, and lots and lots of patience. Even with using the three cheat codes above you'll get sims snapping into odd poses. You just have to take your time, have patience, and keep trying.