restricting weapons when buying only would effectively disable autobuy and rebuy on your server (since i dont think sm can tell what weapons were purchased via those cmds). also, how are you going to stop somebody (or an admin in your case) from just buying 3 awps and giving them away. sry for bad news. i would suggest requesting features like admin immunity in an existing plugin thread.
i agree. i hate running over to pick up a weapon and the sucker disappears in my hands, leaving me to die. what i did for awps (when i used to allow them), is replace them with another effective weapon. maybe something else to request.