What was the whole purpose of producing the space suit for The Impossible Astronaut? Couldn't the Silence achieve their purpose in simpler methods?
(I saw all the episodes, feel free to spoiler in your answers)
Per my answer here;
The Silence needed the suit to physically control River Song. They're aware of the events surrounding his death (e.g. that he's shot by River Song at Lake Silencio on the date in question wearing an Apollo spacesuit) and must have been quite surprised to find that she had no intention of doing so.
Their reaction was to travel further back into time and guide the development of the human race to the point that they'd developed a space suit capable of being used as a physical control device, turning her into a 'people puppet'.
In the episode 'The Impossible Astronaut' River Song is later reported to have said to the Doctor (at the moment of his apparent death):
"I can't stop it - the suit's in control".
As to why they didn't try something less convoluted (e.g. altering the entirety of human history just to get hold of a space suit that they could have easily replicated themselves) the answer is that it's not been explained.
I also think the suit represents that Riversong is kind of in a controlled incubating machine or self preservation armour, being space themed it of course had to be an astronaught suit, it's also potentially the same suite that ages her or twisted her time line against The Doctors as a sort anti Doctor timeline, knowing that Amy and Rory are amongst The Doctors dearest friends, what better way to punish him then by using his friends child as a trained assasin to kill him. And by making sure they never meet properly there after the kill River was to meet him backwards so she new that her task was to kill him, but of course she lived him to much to do so, so the suite can never really control her, when she meets Amy in the suit she's trying to warn Amy, not hurt her.
In a later episode I believe it is stated that they needed to over load the suit to prevent River Song from regenerating and force all her R.E. along with the suits power supplying a single blast killing the doctor. Also the original design of a space suit is based off of a diving suit so it would keep River alive long enough under water to have to regenerate when the time comes; it can also be considered a clue to the time that the doctor needs to go to in order to try to save himself while a diving suit would be too mysterious.