In my opinion it's not good idea.
"крепись,держись" - imply that you are not strong. they are wishes/commands.
They are more like:



"будь сильным" is male-oriented. "будь сильной" is for female subject. Meaning is correct, but I would call it "featureless".
Last two are wrong in syntax (in your case), but anyway they express the same idea in the same way.