the people making this show are obviously not idiots, and do pay attention to details... your last bit about the automation of the button is obvious - it's a part of the plot. dharma has someone pushing the button for a reason. also, i'm an it geek too, i've been programming 12 hours a day for 6 years, and i would not trust a computer to take care of a possible world-ending task with no human intervention... granted, there would be a backup system, you would still want a person there monitoring it constantly, and the best way to do that is to let them think there is no backup system
also, how do you know those computers and tapes do anything at all? maybe they just spin around and flash and beep to make the button pushing people think it's important.
also we don't know much about what happened before and while desmond was there... it's possible everything was set up nicely before desmond got there, and it's also possible that someone snuck in while desmond was out in the forest, or sleeping, and fixed everything up...
also, the fake lookalike is probably because they had a very specific idea of what they wanted the screen to look like. the set designers won't just throw something in there for no reason, they want it all to maintain a certain atmosphere to it, and i guarantee they picked the look of the computer, and of the screen display, to fit their overall vision of the hatch. remember, this is "lost", not "the office"

the mystery and strangeness of it all is extremely important