The first two are completely fine!
"Don't be here, please!" Sounds quite funny to the average English speaker. If the person in question is not there yet but is on their way, you could say "don't come here, please!" However if they were already there, you would just ask them to leave.
"Please leave here" should just be said as "please leave", as if you're asking someone to leave it implies that they're already "here" (there).