For the scytek, you will only need a relay for popping the trunk and/or making the horn honk when the alarm goes off. The siren that comes with it is plenty loud for me.
You will need a few resistors, and some diodes. Those can be acquired pretty cheap at your local radio shack.
http://www.directwholesale.net/diagr...ms.asp?link=DW
I used this site for my wiring diagrams. There also are a few others on the internet.