You might end up "lightening" the marker 
inked "Book 1" if you were to remove the tape. 

I have a few of my cels removed from the nasty 
tape. The sequence number on it has "lightened" 
in the process. But no matter what, I never leave 
tape on my cels.

I remove all of it and store the cel layers in 
separate pockets. Stacking them together might 
flatten the paint. I guess I wanted just as much 
as to see the cel layers together with the 
background, but if that is going to harm the cel, 
I will keep them separated.

Tape left on the background for too long will 
turn brown, brittle and left a sticky patch. 
Removing it will tear off some paper from the 
background... I've tried all ways, but none as 
successful, because I find the background paper 
to be too "soft"... *scratches head* ermm... if 
you know what I mean by that...

Maybe that's just me.

You might also want to send your cel to some 
professionals to get it done. This cel means a 
lot to you...

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-Line Fadings: A trial and error-

I found out a way to keep the costs low and also, 
to reduce line fadings. 

Normally, for a folder, you will get those 
yellow/blue sheets insert in each folder pockets. 
Instead of leaving those behind the cel when 
storing, or some might totally throw it away, you 
can insert those thin sheets in front of the cel.

This will slightly prevent rays from going 
through to your cel. And because it is thin, you 
can actually see what cel is behind it.

Bad point is: 
1. The folder is going to get thicker and 
heavier, so storing cels vertically helps a lot 
in reducing stress...

2. You might not be able to view/admire your 
cels...

Any more recommendations? I would like to know 
besides using UV protective glass...