preserving my cel-how to frame

A lot of people will destroy the background in order to get the cel free from it. If you don't want to destroy the background and you're not willing to pay the $100 or so it will take for SR Labs to do the job, then, yeah, there's not much you can do. Even if the background colors seep into the cel, depending on the background's colors & the cel, it might not be noticeable.

I haven't noticed any line fading with my sketches, but the paper does have a tendency to discolor over time. All you can do is keep it packaged in acid free materials and make sure there's decent air flow in order to prevent deterioration.

A sheet of MicroChamber paper behind the sketch might help prevent the discoloration. That's readily available from archival supplies stores like bagsunlimited.com. Also, be sure you've removed any cellophane adhesive tape, as that will, in time, discolor the paper, especially if it is exposed to light.