Don't make two left hand fuselage sides.....

Since you've already done a few laser cut kits the only thing you're truly adding to the building experience is cutting out your own parts. And the only hint I can think of in that connection is to always cut a hair's width to the outside of the lines. It's easy to sand a little off to make things match or fit but it's not all that easy to make the parts grow if they are too small.

Along that line sandpaper is best used for the vast majority of cases with a backing block to ensure a flat pressure surface.