Got an email today about baggage policy and gear check.
Now I check my passport and find it expires on 11 Oct 2015. On the one hand this gives the required 6 months in hand before expiry. On the other hand, it will be a ten or twenty days short of a full 6 calendar months. I don't know how picky these people will be on the border so I suppose I need to renew may passport pronto - grr!
Secondly I had an email telling me the ESTA visa waiver thing is expiring from the time I got it two years ago (This is my third Boston.) At least that can be done online at https://esta.cbp.dhs.gov
In general I would say that this maintenance mileage is probably enough to get you started, especially if you have been through a marathon plan a few weeks or a couple of months before. For example, the ultraladies newbie 50 km starts at 36 mi/wk and then immediately has a cutback. (Don't be insulted - they have well-respected plans.)
On the other point of minimising number of sessions/wk I'm not too sure but you could look into it with books such as Bryan Powell's "Relentless forward progress" or Hal Koerner's "Field guide to ultrarunning".
Caveat: I've only stepped up to 50 km with this approach, so YMMV and there will be more experienced people out there.
Edit: The second part of your question is covered in chapter 14 of the book "Runner's world run less run faster" which used advice from Hal Koerner. Basically, they say that their marathon programme (FIRST 3+2) can be added to with a few extra miles on long runs to get you to 50 km. To get to 50 miles one can add a fourth run a week and bring in back-to-back weekends.
... Its odds on that anyone racing a HM will be out on the roads the following day, forcing the issue. ...
The plan I follow from a trainer on Garmin Connect actually has two non-running days after a training half at race pace, and only 4 running sessions that week instead of five. I think it pretty likely that people will follow the plan, especially since it tells them they don't need to run
My training programme from Garmin Connect website actually calls for a half at race pace at the end of week 10 of 16. Last year this programme gave me a new pb of about 7 mins better, after a couple of dozen other marathons on other programmes, so I am confident in it. I agree with the majority viewpoint that a half would be fine, in fact a desirable thing to do.
I suppose if I had to find a reservation,I would say: don't get into an all-out struggle with another runner, simply run your own race at race pace for a half. There is a good training effect for the coming marathon from running at this pace.