Max Long Tail
Sorry but I'm not able to provide any helpful info.
Visionman
You can take the Undergroung (Metro) to King's Cross and in there get a Train that will take you to LTN. Additionally, I think it is also possible to go by coach (Bus) with Nationalexpress. Either way, I would allow at least 2 hrs for the trip (via the underground you go to central London then to the other airport, via the coach it depends on much traffic there will be).
No personal experience regarding accommodation but there are lots of hotels nearby LHR, some of which provide courtesy transport to the hotel, and some nearby LTN.
Good luck!!!