For the "Ben" name, I find it has sense. You say that "it dosen't take too much brainpower to know that Ben Kenobi = Obi-Wan Kenobi". Yes, for us, cause "Kenobi" name seems "exotic" to us, but maybe it's a usual name in the Star Wars universe.
If the Galactic Emperor puts me in charge of hunting down and killing the Jedi, and I've got a score to settle with one particular Jedi named Obi-wan Kenobi, you betcherass I'm going to find every person in the Galaxy named Kenobi and everyone named Obi-wan. It doesn't matter if there's trillions of them; that's what computers and data mining are for. To do any less would be criminally negligent. Besides, when people really want to hide -- say, relocated witnesses, or intelligence officers and agents -- do you really think they just change their first name and hope that'll be enough?
Surely, at some point, Obi-wan was visited by some ISB agents or someone like that. He must've just mindwiped them and sent them on their way. Or maybe killed them and falsified their report.