Aye, Mountain Higher is an incredible bit of mountain porn. Superb stuff.
Re the Maratona, there is a ballot, much like the one for the Ride London (minus the charity overload), but I think most Brits do it via Cycling Weekly, who have a bunch of guaranteed spots. You pay a bit extra for that, but it gives you a bit of peace of mind and you can book accommodation safe in the knowledge that you're in. Ian Parr is the guy that looks after it all. He sent round emails the other week for next year, so I think it may be a bit late to get onto the list (he was saying it was oversubscribed as it is), but I'm happy to forward on his email if you want to try and squeeze in.
Regarding the accommodation, we usually book an appartment, so we can do our own cooking and all that. We tend to drive down so have the bikes in the back along with some UK essentials (porridge etc.). There are a number of bike shops in Corvara, which is where the finish is (we usually book a place at the foot of the Campalongo, which is maybe 200m from the finish, you also go past it twice on the ride so it can be handy for supplies etc. if you want to be self-sufficient), but I have no idea about renting bikes there. I didn't get the impression it was akin to Bourg D'Oisan or anything like that, but you might be able to get something.
The other thing of course is that you'd need to get from the airport. It's doable, but for the hassle involved, we tend to just drive down as it's a bit easier, and you can take track pumps and various other handy bits and bobs with you, and of course you can drive out to climbs a bit further afield if you don't fancy mammoth days.