Dean, I stayed in the Frankfurt NH Messe. Directly opposite the expo and the start line. A ten minute walk from the main station, (through the red light district). The hotel was excellent with a decent breakfast. Close to the subway system too. Obviously it was full of runners too so if you are travelling on your own there is always someone to chat to.
ME and a mate are doing it. It was tricky to get to Valencia from the North East. Basically it's the train down to Gatwick and flights direct to Valencia from there. Easy Jet I think we booked with. Basically sorted it out through Expedia.
I did it last year in 3:07 off a PB of 2:58:30. It's certainly flat but I had a bad run hampered by phantom knee pain. I found the pens poorly policed and very cramped with jostling at the start and it didn't seem to thin out for miles. It was also very twisty and turny. It was also raining. Basically I was in a grump from the start and couldn't shake it. Joolska had a fantastic run from memory and broke her sub 3 target.
My advice is get to the front, don't get boxed in and you've got a great chance of a pb.
The city is great though. Fantastic German organisation and efficiency. Our Hotel was right across the road from the start and the expo. Definitely worth doing.