After many discussions with Mr. X, it looks like the new marathon plan is Venice in October. It's a local race for us, so planning will be much easier. Also, it provides me with the right amount of time to rebuild my base (foundational running) so that the hardcore marathon training won't kill me.
All in all, feeling super positive about this plan. Now all I need is someone who wants to buy 2 places in the Edinburgh Marathon... got a few nibblers, but no biters (buyers?) just yet.
Base training on Monday. Woot for enjoyable & relaxed running!