As I'm still a newbie too, I have many of the 
same questions as you do. But here are some of 
the things that I do to protect my cels. 

I try to remove any tape that is stuck on the 
cels and backgrounds only if I think that I can 
do it without damaging them. I never even attempt 
to pull apart stuck layers unless they seem to be 
only very slightly stuck. I separate unstuck 
layers and backgrounds with cel bags to protect 
them and keep them from ever sticking. Also I 
have found that using a Swiffer sheet (the 
magical cloths that go on the end of the Swiffer 
brooms) is a great way to lift dirt and dust off 
of cel layers. And it seems to me to be very 
gentle on the cel. Hope this helps!!

Now, does anyone know a good way to remove the 
little spots of oil that can get on the cel from 
fingers and such?? 

Fever