Question: Ben Affleck first met Uma Thurman at a party just before he was offered and accepted the three year job. Surely he would have recognized her after having his memory wiped even if he could not remember any of the time they spent together.
Answer: Do you remember every person you've ever talked to at a party? Didn't think so. His memory isn't restored back to perfect condition - he's still had three years to forget about details at the party. He remembers things like the origins of the deal because it was important.
Question: I understand how Michael collects things to prompt certain actions after he gets "out", but how does the diamond ring work. Each item serves a purpose. to set off the sprinkler system, etc. but how does he know in advance, the kid would steal the ring? The items were placed in the envelope to "make" things happen (getting off the bus if memory serves me correctly was the point of having the ring stolen.) In the original time line as viewed on the machine, there wouldn't have been a ring for the kid steal it, so how does he know the kid will "take the bait"?
Answer: He has the ability to see what will happen if he changes certain things by looking back in time. He just kept making changes until he got the desired results. He could have added dozens of things until he found something would would force him to get off the bus.
Question: How did those newspaper articles from the future get onto the stamp? Wasn't it possible only to see the future rather than actually travel through time?
Answer: No time travel is necessary. The machine is apparently able to show what ever the viewer wants to see, so Michael Jennings could simply have zoomed in on some newspapers in a newsstand or something and snapped a picture of them.
Question: What is the name of the blond woman which has sex with Ben Affleck at the beginning?
Answer: The name of the character is Rita Dunne. The name of the actress is Kathryn Morris.
Question: Would it have been at all possible for Ben Affleck to obtain the key to the janitors office in the train station and mail it to himself, as he was not allowed to leave the complex he was working in for three years?
Answer: He could have got someone to obtain the key and bring it to him. The same goes for much of the other stuff in the envelope.
Answer: He does recognize Rachel from the party as well as when he when he saw her at Allcom. The only things he doesn't remember are the last three years of his life since starting the project. So, while he does remember her, the three years they spent together while at Allcom are a total blank. This recognition is shown when he meets with Porter who helps him escape.
But later, when he is going through her stuff, he says he doesn't remember her. Also, if he did remember her, he would have known it wasn't her when the imposter was in the restaurant (also no need to have the imposter try to dress like her either).