E60 problems

So, I've decided to take my E60 and put it back on the road but there are a few issues. I need help.

1st, a rear number plate light bulb is gone and fitting a new one doesn't cure it, do I need a BMW Specific bulb?

2nd, there is a driving stability control failure, no ABS, Traction Control, it was plugged by a mate who says its some sensor under the front seats, is this the occupancy sensor?

3rd, the restraint system is showing an error so no Airbags or seat belt tensioners, is this related?

restrain and abs/tc could be related with a bad battery?

The battery is grand though or is it worth replacing?

try to run a diagnose , see what kind of error u'l get and take it from there ?

I've had if done, apparently, but the details are vague from the mechanic.

Maybe the bulb is a damaged wire in the elephant trunking in the boot happened in my car that's an E46 tho not too sure if that issue happens to E60s.

The 3rd issue might be related to occupancy sensor.