I would say that it's unlikely to be the cam sensor as they very rarely give trouble on a V6 and won't prevent the engine from starting.
Likewise, a coil pack connector problem would cause it to still fire on one bank. It's worth taking the scuttle panel off and sealing both the join in the panel above the offside coil pack and the hole where the wiper arm goes through with silicone sealant or similar, as if the plug wells fill with water they will cause a misfire and can destroy the coil pack. But that's not your problem at the moment, IMHO.
Crank sensor is another matter. They do often cause problems although normally the failure mode is that they start failing from hot and more often than not there's a 0335 code stored. I wouldn't rule it out, though.
Immobiliser can cause problems but you'd get a flashing engine management light when you crank the engine in that case.
It might be worth cranking it a few times with the accelerator to the floor. This enables a "flood clear" mode where it disables the fuel injectors. It's possible that, in taking a while to fire, it's flooded the engine.
Other things to check:
Check the fuel pump fuse in the fuel box under the steering column and all the large fusible links in the box above the battery positive terminal.
Get someone to listen in the boot for the fuel pump while cranking to see if it can be heard.
My money is on the crank sensor, though. The wiring to it is close to the back of that coil pack so it could well be that it was disturbed while that was being checked, and it's the wiring to the sensor that fails due to the heat where it is routed close to the oil lines and exhaust manifold.