A code alarm is an audiovox, which is a very fine alarm. I've used many audiovox alarms in the past with no problems at all. I personally use AutoPage, which work absolutely great and virtually never fail.

As for your audio, well... It's not the greatest stuff, but it'll work and it's a good starting point for you. I'd run 1/0 wire to cover all your bases and I always suggest running 3 sets of RCA's so if you ever want to add a 4ch amp everything is already prepared for it.