Focus electric gremlins got me scratching my head

I have a 2008 Focus 1.6 tdci estate, I have an electrical issue that I’m hoping some of you guys & girls might of encountered before. It’s not a pressing issue at the moment as the car is off the road for a while .

So when you turn the key to start the car you have to wait approx 3-5 secs before turning the key otherwise you get nothing, then once started it takes a further 10 seconds then the dash comes alive and cycles and all electricals come on . Literally when you first start the car nothing works , no windows , radio dash lights etc etc then it all comes alive. It’s the same every time never got any worse so far although since I’ve owned it it’s never been on the road yet. Checked fuses & code read but nothing . I found a little mouse nest inside the fuse box and fixed a few wires the little bigger had feasted on , thinking I’d solved it but no lol. I’m leaning towards the bcm but electrics are not my forte really . I hear the focuses have issue with electrics so can someone point in the right direction ?