idle, first check coolant, low coolant causes surging idle
next check/clean IAC
next, remove fast idle thermo valve from bottom of throttle body, remove 3 phillips screws and tighten big flathead inside all the way to seat plunger
horn, check fuses first, then check the actual horns and see if they are there, plugged in, getting power (test light), check grounds
if they are not getting power, then check the steering wheel to see if the switch is even hooked up, aftermarket wheel? jdm wheel?
SRS light could be any number of things
most likely is a jdm wheel with no airbag, just a hunch
could be the srs computer or one of the sensors, will prob need a dealer scan unless one of your local auto stores has a ballin ass scanner and will let you scan your srs code