TBH the only thing you really need is the spoiler. Going down the list of parts...

Screws & caps are generic- can be replaced by any shop.
Trunk spring- only required if you want the boot to lift up when you pull the lever. First gen of the FD Civics doesn't have this when we had the OEM spoiler fitted (mine was dealer fit in 06 at launch)
Spoiler harness- this is the only item you might need. I think it's used when you unplug the brake light, you use this harness to extend the cable and reach the brake light in the spoiler connector. Maybe try fashioning your own? *shrugs*
Sealers- just use double sided tape
Template- can be downloaded off the internet or the installer should be able to figure it out when he looks where the holes on the spoiler are located (it's basically a guide saying where to drill; Mugen use same drill points as well)
Protective tape- just double sided tape