I wouldn't do what you are doing. It looks o.k., 
and I know you did a ton of work! (God knows I 
can't cut out shapes so cleanly) but you can 
tell that the cel scans were cut and that the 
image was placed over another picture. Getting 
backgrounds from screen captures is something I 
have been doing for a while, but the best way to 
make it look clean, and preserve the cel look, 
is to print out the capture after digitally 
removing the character from the background. Then 
scan the print out with the cel on top. It looks 
a lot cleaner that way and preserves the way it 
presents, proving that you own the cel and 
didn't just cut and paste together something. 
Below is a cel and a background that I made 
using a screen capture.