Look a few pages back in the thread where Imy fitted a double-din unit, it wasn't plain sailing but he managed it in the end - some of the fascia kits aren't great and there isn't much room back there. But I have no direct experience I'm afraid.
It's probably easiest to run the mic cable down the passenger side A pillar - remove the glovebox etc and you'll be able to run the cable under the dashboard. There's plenty of guides on taking things apart etc on
www.fordwiki.co.uk but once you get the car you can always ask here
The door cards are easy to remove - there's screws round the edge, one inside the arm rest / handle (you have to remove the little L-shaped insert), one behind a little round plastic blanking insert inside the door pull and one inside another blanking insert where the door mirror is. Then it just lifts off and gives you full access to the speaker.