1. the wipers i dont know about, diagnose like any electrical problem starting with fuses and relays, then the switch check the wires, see if you can bypass the switch, try giving voltage directly to the motor.
2. same as number 1 for the horn. as for the airbag, i think this car is equipped with ' single stage airbags ' which are just as likely to injure you in an accident as they are to save your life.*I AM NOT RESPONSIBLE, DO THIS AT YOUR OWN RISK*. i removed all relays and fuses labelled air bag and disconnected the light in the dash.AGAIN *I AM NOT RESPONSIBLE, DO THIS AT YOUR OWN RISK*
3. rough idle is often air flow / vacuum leak or bad motor mounts. that being said research ' ka24de timing chain rattle' and you will find its fairly normal for these engines to idle rough as the timing chain has too much slack at low rpm. there are permanent fixes for this that i have not done but what i have done that helps is: turn idle up 100 or 200 rpms, this is easy and you can find diagrams in the ' fsm ' section on this website
http://www.nicoclub.com/FSM/Altima/ . also mobil one 5w30 high mileage (about 3 parts to 1 part) regular lucas oil, when change oil run you can try sea foam in the oil, however many think this is snake oil and some say it can ruin seals and pumps. use quality oil filters, i get oem ones from the nissan dealership for 5 dollars, they basically fit any nissan. also premium gasoline, you know those numbers on the gas pump ie 87 89 91 ? these correspond to anti knock rating [aki]. the higher number ' 91 ' is what you want
good luck