I ran this in 2014. I tend to book this sort of thing myself rather than buy a package which tends to work out cheaper. The downside of course is you have to do a bit more research and fend for yourself over the weekend. Found the most difficult bit was working out how to get to the Expo which was down on the coast in one of the old Olympic arenas. Once I'd worked that out everything worked very well and I thought the organisation was excellent. Not the most scenic route and mostly uphill but the finish in the old Olympic stadium is spectacular.
Any central hotel should be fine. I stayed close to Syntagma Square which is one of the locations from where the buses depart to the start at Marathon.