This is pretty much all wrong.
1> Palpatine did not have a "hit list" of other Force users. Ben Kenobi and Yoda were out and about, and there is zero indication there was anyone looking for them. If he knew they were around, he probably would have been hunting them down. Besides this, Luke and Leia were born, and had significant Force potential, and neither Palpatine nor Vader had any clue they even existed. And Vader kinda wanted to know.
2> None of the Jedi could tell that Palpatine was a Force user at all, let alone a Sith master. And it's not like they didn't meet him on the regular.
3> Nobody figured out Dooku had gone Dark Side either, for years. When he was an active Jedi.
You're making up rules the original trilogy and prequels flat out refute. Force users don't sense each other, or at least it's fairly trivial to conceal your Force potential. They can detect force potential in untrained kids, but that's likely because they can feel the Force being manipulated (why else would they need to test Anakin's blood in Phantom Menace?).
What we do know that Force users can sense is significant events like mass deaths. Luke may have felt the stirrings in the Force of a powerful Dark Side user actually USING their power, but that's all he knew. That there was someone, somewhere out there. And yes; Luke fucked up with his school. That's the point. He was arrogant and did not have a handle on his own Dark Side leanings. He is the one who put his students at risk. He knew that. That's why he sent himself into exile.