i have sooooo many extra wires in my S/T its ridiculous (Strobe Lights,system,EMS/FIRE radio, Scanner and a few other things), the only advise i can give you is just to think it out. i cant tell you how many times i had to start over because i didnt think where the wire had to go before i started. just make sure you have access to somewhere to hide the wires before you run anything. plan out where the wires need to go and how you can make it neat. i have my radio mounted at the end of my console, the only difference is that i have a shorty console.
if you are handy, i would suggest taking your console out and making your own. if this is not the case, there are consoles made by companies for radio's and basically anything you want to put in it. we have one of these boxes in our explorer at my EMS company. it looks awesome. if you are going for the best look, i would suggest that. if you post a couple pics of your console and radio i can give you some ideas.
i noticed you said you are installing a "police siren." just want to give you a heads up that if you dont have a permit for that, you really cant use it unless its in a parking lot and such. your state laws may be different so i can be wrong, but in CT, a siren is a big no no. but hey, maybe you are allowed to have one.
if you dont mind me asking, is there an external speaker for the siren? is it a true siren or a JC whitney style type? i was looking into one for fun. thanks