Hello chili.
The display will just be a bulb out.
The Air Bag should be the connection under the seat somewhere, common problem, mine is ok so don't know where to tell you to look but someone here will.
The Air Con though, worries me a bit. You see I have just had to replace the Condenser Radiator on mine (a 1999) yours is of the right age unfortunately to suffer the same problem.
You should budget ?300.00 for this which would be a new Condenser, fitting, testing and a regass. You see with air con if it's not working then it has leaked most probably and a regass will just leak out again.
Here's a pic of where they most commonly leak on D9's i.e 1999 onwards new front end etc.
That is green refrigerant oil leaking from where the condenser has rotted through at the bottom of the plastic housing that hold the electric fan at the front.
I reckon you have got it cheap enough to hopefully get a few bits done to it to make it just right, normally these issues build up and the previous owner gives up and sells out not wanting to part with any more on repairs.
PS. I hate those sellers working from home, they might be the nicest people but something tells you they want to sting you. Hope yours goes well, the 406 is suprisingly trouble free, ask anyone here.