chapagetti

hey guys, i was just wondering what pieces WONT fit. parting out a 2000 civic si coupe, for my 2000 civic hatch (ek/ej6), i heard i cant use the rear bumper, and rear seats.. wondering if i can use the side skirts, they line up like they would fit.. i held em up to the shell and seemed like a match, but this is my first honda so im a complete noob. also, if anyone who is reading this is from WA or know about WA state patrol inspections, i was wondering, if i can buy parts from people online. like if i bought rear seats, or rear hatch, or rear bumper (all of which i need), will i get in trouble? ive asked a few friends and i get mixed answers. one friend told me that its okay if i can get a bill of sale from them with a copy of their drivers lisence.. others said i cant... anyone know?

sorry for the noob questions. any help is much appreciated. thanks in advance.