Rick it sounds like you have the uber rare heated rear seat pads which will be the wires in the rears, the fronts will have heated pads as well which will show up as extra wires/contacts in the multi plug. All Vec C's have seat airbags, your light could be the drivers airbag. Thats an SRi steering wheel, it has HU buttons and Silver inserts but most police dont have these fitted so......the airbag may be miss matched, which would cause the airbag light. Some have one plug and some have two that connect to the CIM.
As for price, if mine was spot on (53 plate SRi) it would barely get £1000. Mods dont really get you anything else over stock price TBH, splitting tends to be the way to go with these to get your money back. I take it the engine is a 2.2? If so it may not have taken much hammer as they used the 3.2 V6 and 3.0CDTi in the pre facelift, the smaller engines were used for CID and training, thats the case up here in Yorkshire anyway. Be aware most things on a Vec C are already hard wired, but have to be switched on in the relevant ECU (the car has about 22 lol) Tech2 is best but Opcom can do most things. Sometimes a little extra loom is needed especially on ex police as they only fitted the minimum so Club spec.