What year is and millage is your r56 mcs
and with out detailed pics it very hard to give the correct advice
I feel your pain and please don't think I am being negative.
but I think it's going to turn into a can of worms,
I have seen so many people get deep in to these and the cost rockets it's not a fixed price job, because you can't test much till you get it 75-80% finished then you my have to take it apart to trace electrical faults, boxes, looms etc
Personally if it was me doing this job, I would find out where the fire started first thing.
I know you say it started in the engine bay wiring some where, but my concern would be if the engine loom has been damaged by fire it will have caused shorts in other parts of the loom causing damage to the body loom all over the place which is possible it my also have damaged the cars computers there are quite a few and the all talk to each other and are coddled to each other as well.
My second thought for the fire would be has any warranty work been carried out like hpfp, aux water pump. If the fire was caused by this I would be straight on to mini as it might have been a faulty component . But you would have to be shore ie a proper vehicle report.
Personally if the heat cracked the windshield I would say there's a good chance the bulk head my have been damage the big problem is once you heat this metal it goes soft and looses all it's strength it may look ok but it's not, I think when you add up everything it's going to make it uneconomical to repair and I really hate to say that I try to save everything I can but it's safety first with me.
I personal think you are going to have a bill for 4 to 6k from what you describe if your lucky and your car my not be 100% safe at the end of that, and tbh 4-6k is if you use second hand parts, and dont have to start fixing other things you find as you go which you will
Personally I would advice you to save your money and a massive headache and part out the good parts on your car and buy another one or clam on your insurance.
Really sorry to sound so negative, I expect you fell sick about it anyway.