River Song's first meeting with the Doctor

It was suggested way back in Silence in the Library that River and the Doctor are having a relationship in opposite directions.  This is a cool idea - a mysterious woman from the Doctor's future who knows him intimately (or at least that's what's implied) but who he's never met?  Cool!  And to have their timelines running in reverse relative directions, so each time they meet, it's the next time for the Dr and the previous time for River?  That's cool.  A pain to stick with (so some wiggle room is required) but cool.

But this would surely mean that the first time River meets the Dr should be the last time the Dr meets River - and the episode Let's Kill Hitler implies otherwise.  Or does it?

At the start of the episode, Amy and Rory get the Doctor's attention by drawing a massive crop circle that he spots in a paper some time in the future.  But which Doctor is it?  It's somewhat taken for granted that it's the same Doctor that we last saw in A Good Man Goes to War, but how do we know that he hasn't been around and had lots of adventures since then?  What if this is the Doctor at the end of his time, aged 1300+ ?

Then the episode takes on a different tone - when River poisons him, and there's no known cure for the poison, he hops in the TARDIS and goes to get help (the Doctor from Amy and Rory's wedding?  Or from the end of the season episode which is apparently something to do with the wedding of River Song?) then heads off to meet the girl on the edge of the lake and gets shot (the Impossible Astronaut).

The timing works (32 minutes until he's dead, and he's in Impossible Astronaut for less than 32 minutes before being shot iirc) and the change of outfit seems odd otherwise, given how that was a big thing about last season (with the Doctor's jacket in the Time of Angels).  The only questions that then remain are: was it even the real Doctor (I thought it would be the ganger Doctor that was killed on the lake edge - but maybe he's the Doctor that keeps on?) and what happened to River's Regenerations (could the Doctor have taken them away from her, knowing that she won't need them?  Could that let him somehow survive being shot on the edge of the lake?  Could it give him more than 13 lives?).