Managed my first IM distance swim last night - 4.2km in 1:47. That should put me safely inside the time cutoff at Outlaw, which is a great relief. (The 4.2km on a swim lap of 800m shows that I'm taking my usual detours to inspect coots' nests, count the pondweed and shake off any pursuing enemy submarines!)
See if there are any Sportives around where you are as well - they usually carefully plot the route on quieter roads, and there will be people around to ride with. And since they are not against the clock, it's a calmer atmosphere and you can enjoy the ride.
Nice one, Booo - sounds as if you've done your preparation work nicely. Take the confidence from that to the day itself.
I'm planning the full distance swim on Thursday, and I'll be happier once I've nailed that. I don't have a marathon on board, but I'm less worried about that. I can't drown on a marathon! Bike should be OK I think - and I laughed about you getting a support call while riding, as I've nearly been there myself. Do Boardman or Giant do a bluetooth kit for bikes yet?