Tircha ditziburah / alarm clock and timer on shabb

Question

Why do we wait for the Rabbi to finish shema and shmoneh esreh before the shiliach tzibur continues? Shouldn't we wait for the majority to finish instead of waiting for everyone to finish, 4 minutes and then the rabbi, and then start? What about tircha detziburah? May I set my alarm clock to go on on shabbat, the kind that has the radio going on. May a timer be set for any and everything?