[sly]

I just have a Forte, not sure which drivers side airbag you mean. If you mean the steering wheel one, yes leave it there when you drop the wheel. OTOH my manual says to take out the passenger's one above the glovebox fairly early on. You have to break the clips holding the panel above the glovebox. You'll need a reply from someone who's done this to get the ins and outs of it.

The heater box... yeah. That's why I took my dash out. Paid a workshop hundred$ to change my leaking heater core only to have the new one start leaking after 6 weeks : If you have to change the heater box, you need to drive the car to someone who can degas the aircon before you pull so much out the car is undriveable (or get a mobile aircon service to come to you if too late :sm_headba ). When the dash is back in you get it regassed obviously...

Yeah the crash sensor is bolted to the top of the transmission tunnel, you have to take out the floor console... between the seats... to get to it. Only 4, maybe 6 screws IIRC.

Best advice I can give you is get a manual, around $40-50 will save heaps of headaches on a job like this, I'm sure I don't remember all the ways this job can bite you... Ellery's or Gregory's probably. My Haynes manual was written when AU1 was fresh, has a lot of carry over from EF/EL that is wrong for the AU. If you get a Haynes get a later one written for AU1,2 & 3... assuming they are better.